Category: Corrosion Engineering Objective Questions

250+ TOP MCQs on Modern Theory Principles – Passivity and Answers

Corrosion Engineering Multiple Choice Questions on “Modern Theory Principles – Passivity”.

1. Which of the following is/are correct regarding passivation?
a) It is defined as the loss of reactivity at certain conditions
b) Usually results in the formation of the oxide layer
c) The corrosion rates are relatively low
d) It is defined as loss of reactivity at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low

Answer: d
Clarification: Passivation is defined as the loss of reactivity of metals/alloys at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low.

2. The passive state of a metal is often relatively unstable and subject to damage.
a) True
b) False

Answer: a
Clarification: Passivation is the loss of chemical reactivity of a metal due to the formation of the oxide layer. It is relatively unstable and subject to damage. Chemical properties, wear resistance and thickness are the factors for the stability of the passive layer.

3. Which of the following is/are the metal/alloys that demonstrate active-passive transitions?
a) Iron and stainless steels
b) Nickel and its alloys
c) Iron, stainless steels, nickels, titanium, and its alloys
d) Titanium and its alloys

Answer: c
Clarification: Metals/alloys that demonstrate active-passive transitions is/are:

  • Iron and stainless steels
  • Nickel and its alloys
  • Titanium and its alloys
  • Chromium
  • Aluminum and its alloys.

5. Which of the following is/are correct regarding the active region of metals?
a) Corrosion rates increase exponentially
b) Corrosion rates increase linearly
c) It follows typical Tafel behavior
d) It follows typical Tafel behavior and corrosion rates increases exponentially

Answer: d
Clarification: Active region is the first stage of active-passive transition in which the corrosion rates increase exponentially and it follows typical Tafel behavior.

6. The Trans passive region is the region in which the corrosion rate increases with an increase in potential.
a) True
b) False

Answer: a
Clarification: Trans passive region is the last region of active-passive transitions of metal in which the corrosion rate increases with an increase in potential. It is formed due to the instability of the passive layer at that high potentials.

7. Which of the following is/are the important characteristics of active-passive transitions of a metal?
a) Passive potential (Epp)
b) Critical anodic current density (i­c)
c) Passive potential (Epp) and Critical anodic current density (i­c)
d) Neither passive potential nor critical anodic current density

Answer: c
Clarification: Passive potential is defined as the potential of a system at which the passivation of metal is starts whereas critical anodic current density is defined as the current density at which passivation of metals starts.

9. Which of the following metal doesn’t possess a trans passive region?
a) Iron
b) Titanium
c) Nickel
d) Aluminum

Answer: b
Clarification: Typical active-passive transitions metals possess active region, passive region, and trans passive region. Whereas titanium doesn’t possess trans passive region is due to the formation of a more protective titanium oxide film structure.

10. Which of the following metals/alloys passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen?
a) Copper
b) Titanium
c) Stainless steels and titanium
d) Nickel

Answer: b
Clarification: Stainless steels and titanium passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen. A decrease in passive potential and critical current density is the driving force for the spontaneous passivation.

250+ TOP MCQs on Effect of Temperature and Corrosive Concentration and Answers

Corrosion Engineering Interview Questions and Answers for freshers on “Effect of Temperature and Corrosive Concentration”.

1. The rate of chemical reaction increases with an increase in temperature.
a) True
b) False
Answer: a
Clarification: Temperature increases the rate of almost all the reactions because it increases the kinetic energies of atoms or ions. This increase in kinetic energy makes them react to each other to get stable products. It also increases the mobility of ions in the electrolyte.

2. What is the corrosion rate behavior of curve A with the increase in temperature, described in the given figure?

a) Constant
b) Exponential increase
c) Exponential decreases
d) Slightly decreases
Answer: b
Clarification: Curves A and B represent the corrosion behavior of different materials with an increase in temperature. Here curve A indicates the exponential increase in corrosion rate with the temperature. Example: Iron in hydrofluoric acid.

3. What is the corrosion rate behavior of curve B with the increase in temperature, described in the given figure?

a) Exponential increase
b) Exponential decrease
c) Constant up to high temperatures
d) Slightly decreases
Answer: c
Clarification: Here curve B indicates the uniform corrosion rate up to very high temperatures, this is due to the formation of protective oxide layers. At very high temperatures, it results in the transformation of trans passive region which increases the corrosion rate exponentially.

4. In which of the following reactions, we observe the exponential increase in corrosion rate with an increase in temperature?
a) 18Cr-8Ni in H2SO4
b) 18Cr-8Ni in HNO3
c) Ni in NaOH
d) Monel in HF
Answer: a
Clarification: Stainless steel (18Cr–8Ni) in sulfuric acid will corrode exponentially with the increase in temperature. Whereas stainless steel in nitric acid, nickel in sodium hydroxide, monel for hydrofluoric acid are the best corrosion-resistant materials in respective mediums and suffer less corrosion with the increase in temperature.

5. In which of the following reactions, we observe the unaffected corrosion rate with the increase in temperature?
a) 18Cr–8Ni in HNO3
b) 18Cr-8Ni in H2SO4
c) Ni in HCl
d) Fe in HF
Answer: a
Clarification: Stainless steel (18Cr–8Ni) in the HNO3 medium will have a negligible effect on the corrosion rate with the increase in temperature. It forms a stable oxide layer and avoids the exposure of a corrosive atmosphere to the metallic surface. It is stable up to very high temperatures.

6. What is the corrosion rate behavior of curve B with the increase in corrosive concentration, described in the given figure?

a) Exponential increases
b) Exponential decreases
c) Constant
d) First increases and then decreases
Answer: d
Clarification: The given figure represents the corrosion behavior of different materials with an increase in the concentration of the corrosive medium. Curve B represents the group of materials where the corrosion rate increases rapidly at first and then decreases with increases in corrosive concentration. This is due to the 1. formation of the passive layer 2. decrease in the ionization of acids.

7. What is the corrosion rate behavior of curve A with the increase in corrosive concentration, described in the given figure?

a) Almost constant
b) Exponential increase
c) Exponential decrease
d) First increases and then decreases
Answer: a
Clarification: Curve A represents the group of materials in which an increase in corrosive concentrations has a negligible effect on it until very high concentrations are reached. This is due to the formation of the passive layer. After that, it results in mechanical damage at very high corrosive concentrations.

8. The concentration of the corrosive medium increases with the increase in impurity ion concentration.
a) True
b) False
Answer: a
Clarification: Concentration of corrosive medium depends on the concentration of impurity ions present in it. General impurities are dissolved oxygen, ferric ions, and many other metal oxides.

9. In which of the following reactions, we observe an increase in corrosion rate with the increase in corrosive concentration?
a) 18Cr–8Ni in HNO3
b) Ni in NaOH
c) Pb in H2SO4
d) Fe in H2SO4
Answer: d
Clarification: Iron in sulfuric acid, the corrosion rate of iron increases at first and then it decreases with an increase in corrosive concentration. This is because, at low concentrations, iron will dissolve in sulfuric acid whereas at high concentrations it forms a passive layer on the sample surface.

10. In which of the following reactions, we observe the constant corrosion rate even with the increase in the corrosive concentration?
a) Fe in H2SO4
b) Ni in NaOH
c) Al in acetic acid and HNO3
d) 18Cr–8Ni in H2SO4
Answer: b
Clarification: Nickel in caustic soda is the best corrosive resistant material at various corrosive concentrations. Thus, it shows a negligible change in the corrosion rate even with the increase in the corrosive concentration.

Corrosion Engineering for Interviews

250+ TOP MCQs on Eight Forms – Hydrogen Damage and Answers

Corrosion Engineering Multiple Choice Questions on “Eight Forms – Hydrogen Damage”.

1. Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen.
a) True
b) False
Answer: a
Clarification: Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen. And hydrogen damage can be classified into four types based on the mechanism of failure.

2. Which of the following is/are the types of hydrogen damage?
a) Hydrogen blistering
b) Hydrogen embrittlement
c) Decarburization
d) Hydrogen blistering, hydrogen embrittlement, and decarburization
Answer: d
Clarification: Classification of hydrogen damage:

  • Hydrogen blistering
  • Hydrogen embrittlement
  • Decarburization
  • Hydrogen attack.

3. What is meant by hydrogen blistering?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: a
Clarification: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids. Initially, hydrogen atoms diffuse into metal and react with each other to form a hydrogen molecule.

4. What is meant by hydrogen embrittlement?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: b
Clarification: Hydrogen embrittlement refers to the loss of ductility and strength of a metal due to the formation of brittle metal hydrides. Strong hydride forming metals such as titanium, results in brittle fracture.

5. Which of the following types of hydrogen damage processes are high-temperature processes?
a) Hydrogen blistering and hydrogen attack
b) Hydrogen attack and Decarburization
c) Decarburization and hydrogen embrittlement
d) Hydrogen attack only
Answer: b
Clarification: Hydrogen attack and decarburization are high-temperature processes. Decarburization refers to the removal of carbon from metal, is often produced by moist hydrogen at high temperatures. Hydrogen attack refers to the interaction of hydrogen and metal at high temperatures.

6. Which of the following industries has a major concern on hydrogen blistering?
a) Petroleum industry
b) Chemical manufacturing industries
c) Oil and natural gas refineries
d) Oil and natural gas refineries, petroleum and chemical manufacturing industries
Answer: d
Clarification: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids.
Industries that have a major concern on hydrogen blistering are:

  • Petroleum industry
  • Chemical manufacturing industries
  • Oil and natural gas refineries
  • Welding workshops.

7. Which of the following type of compounds act as an inhibitor for hydrogen-ion reduction?
a) Sulfide ions
b) Phosphorous compounds
c) Arsenic compounds
d) Sulfide ions, phosphorous and arsenic compounds
Answer: d
Clarification: Hydrogen atoms diffuse into steel and other metals, which results in hydrogen blistering and hydrogen embrittlement. These inhibitors such as sulfide ions (polysulfide ion), phosphorous, and arsenic compounds reduce the rate of hydrogen-ion reduction.

8. Which of the following type of corrosion is depicted in the given figure?

a) Filiform corrosion
b) Hydrogen embrittlement
c) Hydrogen blistering
d) Uniform corrosion
Answer: c
Clarification: Hydrogen blistering is depicted in the given figure. It refers to the local deformation of metal with the entrapment of hydrogen molecules in the metal voids.

9. Which of the following type of corrosion is depicted in the given figure?

a) Hydrogen blistering
b) Hydrogen embrittlement
c) Filiform corrosion
d) Selective leaching
Answer: b
Clarification: Hydrogen embrittlement is depicted in the given figure. It refers to the loss of ductility and tensile strength of metal due to the formation of the respective metal hydride.

10. Which of the following metal is highly susceptible to hydrogen embrittlement?
a) Titanium
b) Nickel
c) martensitic iron-base alloys
d) Titanium and martensitic iron-base alloys
Answer: d
Clarification: Hydrogen embrittlement refers to the brittle cracking failure of reactive metals due to the formation of metal hydrides. Titanium, ferritic, and martensitic iron-base alloys are susceptible to hydrogen embrittlement.

11. Which of the following type of corrosion in which corrosion occurs due to the presence of hydrogen sulfide?
a) Hydrogen embrittlement
b) Hydrogen blistering
c) Sulfide stress corrosion
d) Erosion corrosion
Answer: c
Clarification: Sulfide stress cracking occurs in the presence of water and hydrogen sulfide. It is highly concerned with petroleum industries and oil refining industries.

12. Which of the preventions is/are the preventions of hydrogen blistering?
a) Use of clean steel instead of rimmed steel
b) Applying metallic, inorganic and organic coatings
c) Use of substituting alloys such as nickel-based alloys
d) Use of clean steel instead of rimmed steel, applying metallic, inorganic and organic coatings and use of nickel-based alloys
Answer: d
Clarification: Preventions of hydrogen blistering are:

  • Use of clean steel instead of rimmed steel
  • Applying metallic, inorganic and organic coatings
  • Use of substituting alloys such as nickel-based alloys
  • Removing poisons such as sulfides, arsenic compounds, cyanides, and phosphorus ions.

13. Which of the following is/are the preventions of hydrogen embrittlement?
a) Baking of steels at low temperatures (200°F–300°F)
b) Alloying with nickel or molybdenum reduces susceptibility
c) Practicing proper welding with low hydrogen welding rods
d) Baking of steels at low temperatures, alloying with nickel or molybdenum reduces susceptibility and practicing proper welding with low hydrogen welding rods.
Answer: d
Clarification: Preventions of hydrogen embrittlement are:

  • Baking of steels at low temperatures (200°F–300°F)
  • Alloying with nickel and molybdenum reduces susceptibility
  • Practicing proper welding with low hydrogen welding rods.

250+ TOP MCQs on Mineral Acids – Sulfuric Acid and Answers

Corrosion Engineering Multiple Choice Questions on “Mineral Acids – Sulfuric Acid”.

1. Which of the following is/are the examples of mineral acids?
a) Sulfuric acid and nitric acid
b) Hydrochloric acid and hydrofluoric acid
c) Sulfuric, nitric, hydrochloric, hydrofluoric and phosphoric acid
d) Sulfuric, nitric, hydrochloric and hydrofluoric acid

Answer: c
Clarification: Mineral acid or inorganic acid is the acid derives from one or more inorganic compounds on dissolution with water. This includes sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid.

2. Which of the following acid is produced relatively higher than other acids?
a) Nitric acid
b) Sulfuric acid
c) Phosphoric acid
d) Hydrofluoric acid

Answer: b
Clarification: Sulfuric acid is produced relatively higher than other acids. The chemical formula for sulfuric acid is H2SO4. It is produced by absorbing water into oleum.

3. What are the principal uses of sulfuric acid?
a) Production of hydrochloric acid
b) Manufacturing of dyes, fertilizers, and drugs
c) Pickling of steels and other metals
d) Production of hydrochloric acid, manufacturing of dyes, fertilizers and drugs and pickling of steels

Answer: d
Clarification: Principle uses of sulfuric acid are:

4. Which of the following method is used to produce sulfuric acid?
a) Contact process
b) Ostwald process
c) Solvay process
d) Haber process

Answer: a
Clarification: Sulfuric acid is produced by the contact process or leads chamber process. It is produced by absorbing SO3 with water. This process accounts for 70% of world production.

5. Which of the following statements is/are true regarding the contact process?
a) Conversion of sulfur dioxide to sulfur trioxide takes place
b) Vanadium oxide is used as a catalyst
c) It accounts for 70% of the world’s production
d) Conversion of sulfur dioxide to sulfur trioxide takes place in the presence of vanadium catalyst and it accounts for 70% world’s production

Answer: d
Clarification: Contact process:

6. Which of the following concentration of sulfuric acid in which the corrosion rate of steel is minimum?
a) Less than 30%
b) Greater than 70%
c) 30% – 70%
d) above 110%

Answer: b
Clarification: Ordinary steels are widely used for various concentrations of sulfuric acid greater than 70% purity. Dilute acids attack steel very rapidly and result in faster degradation.

7. Which of the following is/are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid?
a) High velocity
b) Temperature of acid
c) Aeration
d) High velocity, temperature, and aeration

Answer: d
Clarification: High velocity, the temperature of acid and aeration are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid (>70%).

8. Which of the following metal is not corrosion resistant to sulfuric acid?
a) Grey cast iron
b) Duriron
c) Durimet 20
d) Lead

Answer: a
Clarification: Grey cast iron is not corrosion resistant to sulfuric acid as it penetrates the metal along with the graphite flakes. Though the corrosion rates are small but the metal may split open in service.

9. Lead is used extensively for sulfuric acid in the lower concentration ranges (<70%).
a) False
b) True

Answer: b
Clarification: Lead is used extensively for sulfuric acid in the lower concentration ranges (<70%). It is not recommended above 70% purity is due to the solubility of lead sulfate surface film in the acid.

10. Which of the following is/are the applications of Duriron because of its corrosion resistance and inherent hardness?
a) To manufacture pumps, valves, and fans
b) To make heat exchangers
c) Impressed–current anodes
d) To manufacture pumps, valves, fans, heat exchangers and impressed-current anodes

Answer: d
Clarification: Duriron is high-silicon cast iron with high corrosion resistance and inherent hardness. It is used to manufacture pumps, valves, fans, heat exchangers, and impressed-current anodes.

11. Which of the following alloying elements are not recommended in the sulfuric acid environment?
a) Chromium
b) Nickel
c) Molybdenum
d) Nickel and molybdenum

Answer: c
Clarification: Alloying elements are added in base metal to exhibit certain specific properties such as corrosion resistance, thermal properties, or mechanical properties. Here molybdenum is not recommended as an alloying element in high-silicon cast iron for sulfuric acid application.

250+ TOP MCQs on Modern Theory Applications – Predicting Corrosion Behavior and Answers

Corrosion Engineering Questions on “Modern Theory Applications – Predicting Corrosion Behavior”.

1. Which of the following is/are the applications of mixed-potential theory?
a) Permit prediction of complex corrosion behavior
b) To develop new corrosion prevention methods
c) To develop new rapid corrosion rate measurement
d) Permit prediction of complex corrosion behavior, to develop new corrosion prevention methods and to develop new rapid corrosion rate measurement

Answer: d
Clarification: Applications of the mixed-potential theory are:

  • Permit prediction of complex corrosion behavior
  • To develop new corrosion prevention methods
  • To develop new rapid corrosion rate measurement.

2. Which of the following is/are correct when oxidizing agents are added to a corrosion system containing a non-passivating metal?
a) Rate of corrosion decreases after certain potential
b) Rate of corrosion increases with increase in oxidizers concentration
c) Rate of corrosion increases after certain potential
d) Results in the formation stable oxide layer

Answer: b
Clarification: The rate of corrosion increases with increase as the concentration of oxidizing agents containing non-passivating metal. It is due to the reduction of oxygen on the surface of the metal and due to the absence of an oxide layer.

3. The corrosion rate is usually dependent at low velocity whereas at high velocities it becomes independent.
a) True
b) False

Answer: a
Clarification: Corrosion rate is usually dependent at low velocities whereas at high velocities it becomes independent. It is due to enough availability of ions at the interface and thereby it depends on activation energy.

4. Which of the following type of polarization has a negligible effect on velocity?
a) Concentration polarization
b) Activation polarization
c) Concentration polarization and Activation polarization
d) Neither concentration nor Activation polarization

Answer: b
Clarification: Activation polarization is the mechanism of polarization in which the activation energy of reactants at the interface is the driving force. It has a negligible effect on velocity as it is independent of diffusion of ions in the bulk solution.

5. Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for hydrogen evolution but not due to the reversible potential of the platinum-platinum ion electrode.
a) True
b) False

Answer: a
Clarification: Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for evolution but not due to the reversible potential of the platinum-platinum ion electrode. Notably, platinized platinum has the highest exchange current density for hydrogen evolution.

6. The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum.
a) False
b) True

Answer: b
Clarification: The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum. It is due to the exchange current density of hydrogen evolution, as the galvanic tests are usually conducted in an acidic environment.

7. In a galvanic couple, the corrosion rate of the metal with active corrosion potential is accelerated whereas the corrosion rate of noble metal retards preferentially.
a) True
b) False

Answer: a
Clarification: In a galvanic couple, one metal acts as the anode (active corrosion potential), and its corrosion rate is accelerated whereas other acts as the cathode (noble metal) and its corrosion rate are retards preferentially.

8. Which of the following metals that are spontaneously passivated on coupling with platinum?
a) Titanium
b) Chromium
c) Titanium and Chromium
d) Neither titanium nor chromium

Answer: c
Clarification: Titanium and chromium metals are the metals that are spontaneously passivated on coupling with platinum. It is due to the mixed potential of galvanic couples lies in the protection region of the passive region.

9. Which of the following is/are correct regarding the potentiostat method?
a) It is a polarization technique that allows for controlled polarization
b) It works on controlling voltage between a working and reference electrode
c) It is a corrosion analysis method
d) It is a corrosion analysis technique method that allows for controlled polarization and it works on controlling voltage between a working and reference electrode.

Answer: d
Clarification: It is a corrosion analysis technique method that allows for controlled polarization and it works in controlling voltage between a working and reference electrode.

250+ TOP MCQs on Principles – Effect of Galvanic Coupling and Answers

Corrosion Engineering Multiple Choice Questions on “Principles – Effect of Galvanic Coupling”.

1. The effect of Galvanic Coupling is due to the contact of dissimilar metals in a conductive electrolyte.
a) True
b) False
Answer: a
Clarification: If two dissimilar metals are placed in contact with each other in a conductive electrolyte, the potential difference produces electron flow between them. This results in the acceleration of preferential anode dissolution. This is known as the effect of Galvanic coupling.

2. What are the factors that affect Galvanic coupling?
a) Type of metals
b) Relative size of electrodes
c) Environmental conditions
d) Types of metals, the relative size of electrodes and environmental conditions
Answer: d
Clarification: Metal combinations used for galvanic contact will affect based on the potential difference between them. Relative size of electrodes, environmental conditions such as temperature, humidity and salinity alter the chemical kinetics of the reaction.

3. Preferential cathode and anode are formed based on the potential value of a metal electrode.
a) True
b) False
Answer: a
Clarification: Electrode with relatively high reduction potential preferentially act as a cathode and the other electrode will act as an anode. The effect of galvanic coupling can be minimized by selecting metal combinations with less potential difference.

4. Which of the following type of corrosion is depicted in the given figure?

a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Crevice corrosion
Answer: c
Clarification: Galvanic corrosion (dissimilar metal corrosion) is an electrochemical corrosion in which preferential anode will corrode rapidly due to the effect of galvanic coupling.

5. In which of the following cases, we observe the galvanic effect?
a) Bolts and Nuts metal joining’s
b) Piping arrangements
c) Machinery of a different metal combination
d) Bolts and nuts metal joining’s, piping arrangements and machinery of a different metal combinations
Answer: d
Clarification: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. The corrosion caused due to galvanic effect is known as galvanic corrosion. It can be usually observed at bolts and nuts metal joining’s, piping arrangements and machinery of different metal combinations.

6. What is the abbreviation of SHE?
a) Substitute hydrogen electrode
b) Standard hydrogen electrode
c) Significant hydrogen electrode
d) Standard hydride electrode
Answer: b
Clarification: SHE means a Standard hydrogen electrode. It is used to calculate the potential of other elements by arbitrarily defined as zero. The standard conditions of SHE is 1 atm pressure of H2 gas, 25°C temperature and non-corroding conditions for pure metals.

7. Which of the following are Reference electrodes?
a) Standard hydrogen electrode
b) Calomel electrode
c) Silver electrode
d) Standard hydrogen electrode and a calomel electrode
Answer: d
Clarification: In EMF series all metals are referenced against the hydrogen electrode (H2/H+) which is arbitrarily defined as zero. This is known as the Standard hydrogen electrode (SHE). The saturated calomel electrode also acts as a reference electrode based on the reaction between elemental mercury (Hg) and mercury(I) chloride (Hg2Cl2). And the electrode potential value of the calomel electrode is +0.241 V.

8. Which of the following is/are the characteristics of a Galvanic series?
a) Used only for pure metals
b) Less accurate prediction than EMF series
c) Includes active and passive potentials of a metal
d) Measured only at room temperature
Answer: c
Clarification: Galvanic series is the arrangement of various engineering materials (pure metals and alloys) in a decreasing reduction potential value in seawater. Galvanic series is more accurate than EMF series and it can be measured at various temperatures of a specific medium. It includes the active state potential and passive state potential of a metal.

9. Which of the following is/are the preventions of the galvanic effect?
a) Insulating dissimilar metals
b) Selection of close metal combinations in a galvanic series
c) Neglecting area effect
d) Insulating dissimilar metals and selection of close metal combinations in a galvanic series
Answer: d
Clarification: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. It can be minimized by insulating dissimilar metals with non-conductive materials. And it can be reduced by the selection of close metal combinations in a galvanic series.

10. Which of the following effect is described in the given figure?

a) Crevice
b) Pitting
c) Beneficial galvanic effect
d) Erosion
Answer: c
Clarification: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. Here beneficial galvanic effect takes place as zinc is corroding preferentially by protecting steel.