Category: Class 12 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Solid State Electrical Properties”.

1. Metals are good conductors of heat and electricity. This property is conferred by _______ bonds.
a) covalent
b) ionic
c) metallic
d) hydrogen
Answer: c
Clarification: Metallic bonds are formed between positive metal ions and the sea of delocalized electrons. This bond is stronger than covalent and ionic bonds. Due to the mobility of electrons, conduction of heat and electricity is feasible.

2. Which of the following properties holds true for a metalloid?
a) Poor conductors of heat and electricity
b) Malleable
c) Ductile
d) Non-brittle
Answer: a
Clarification: Metalloids have properties intermediate to those of metals and non-metals. They are non-malleable, non-ductile and brittle. They are poor conductors of heat and electricity as compared to metals, but are better conductors than non-metals.

3. According to the band theory, increase in number of atoms participating in crystal formation leads to ________ in number of molecular orbitals containing electrons.
a) decrease
b) increase
c) no change
d) either increase or decrease, depending upon the size of the atoms
Answer: b
Clarification: The band theory assumes that atomic orbitals of the atoms of the crystal combine to form molecular orbitals which are spread over the whole crystal structure. Hence, the number of atoms is directly proportional to the number of molecular orbitals formed.

4. For a metallic crystal, which band do the delocalized electrons occupy?
a) Conduction band
b) Valence band
c) Both, conduction and valence bands
d) There are no delocalized electrons
Answer: a
Clarification: A metallic crystal has valence electrons in the valence band and free moving, delocalized electrons in the conduction band. For a metal, these two bands are very close to each other.

5. A substance containing one band completely filled with electrons and other band completely empty, but with a possibility of the empty band becoming populated, behaves as a _________
a) metal
b) non-metal
c) semiconductor
d) metal and non-metal
View Answer

Answer: c
Clarification: Semiconductors have completely filled valence bands and completely empty conduction bands. The energy gap between the two bands is relatively small and can be overcome by supplying heat, which excites some electrons to the conduction band, thus allowing the conduction of electricity.

6. Label the diagram correctly.

a) 1-Non metal, 2-Semiconductor, 3-Metal
b) 1-Semiconductor, 2-Non metal, 3-Metal
c) 1-Metal, 2-Semiconductor, 3-Non metal
d) 1-Metal, 2-Non metal, 3-Semiconductor
Answer: c
Clarification: Energy gap is very less (may even be absent) for metals, very huge for non metals and intermediate (small) for semiconductors.

Chemistry Multiple Choice Questions on “Electrochemistry – Fuel Cells”.

1. A fuel cell is a type of electrochemical cell.
a) True
b) False
Answer: a
Clarification: Fuel cells are the devices which convert the energy produced during the combustion of fuels (chemical energy) like hydrogen, methane, methanol etc. directly into electrical energy. Hence, a fuel cell is a type of electrochemical cell.

2. Which of the following is used as an electrolyte in an H₂-O₂ fuel cell?
a) KOH
b) NH₄OH
c) Fe(OH)₂
d) Cu(OH)₂
Answer: a
Clarification: The general design of the H₂-O₂ fuel cell consists of porous carbon electrodes containing suitable catalysts (generally finely divided platinum and palladium) incorporated in them. Concentrated KOH or NaOH solution is placed between the electrodes to act as the electrolyte.

3. Which of the following can be used as fuel in a fuel cell?
a) Nitrogen
b) Argon
c) Hydrogen
d) Helium
Answer: c
Clarification: Hydrogen is the simplest element. It is also abundantly available in the universe. Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. Hence, it used in a fuel cell.

4. Which of the following is not a fuel cell?
a) PEM cell
b) Direct methanol cell
c) Solid oxide cell
d) Daniell cell
Answer: d
Clarification: Polymer electrolyte membrane (PEM) cell, direct methanol cell and solid oxide cell are all types of fuel cells. Daniell cell is a primary galvanic cell with a copper cathode and a zinc-amalgam anode. Daniell cell is a reversible cell.

5. Which of the following is not produced in an H₂-O₂ fuel cell?
a) Electricity
b) Pollutants
c) Heat
d) Water
Answer: b
Clarification: Fuel cells convert the chemical energy of fuel into electricity through combustion. Since combustion is an exothermic reaction, heat is evolved. The overall reaction in an H₂-O₂ cell is:
2H₂ (g) + O₂ (g) → 2H₂O (l)
Thus, water is also produced.

6. Which of the following is supplied to the cathode of a fuel cell?
a) Hydrogen
b) Nitrogen
c) Oxygen
d) Chlorine
Answer: c
Clarification: A fuel cell is composed of an anode, cathode, and an electrolyte membrane. A typical fuel cell works by passing hydrogen through the anode of a fuel cell and oxygen through the cathode.

7. Who invented the first fuel cell?
a) Francis Bacon
b) Thomas Grubb
c) Leonard Niedrach
d) William Grove
Answer: d
Clarification: The first fuel cell was conceived by Sir William Robert Grove in 1839. He mixed hydrogen and oxygen in the presence of an electrolyte and produced electricity and water. The fuel cell he made used similar materials to today’s phosphoric acid fuel cell.

8. What is the maximum theoretical energy efficiency of a fuel cell?
a) 100%
b) 69%
c) 50%
d) 83%
Answer: d
Clarification: E°_cell of an H₂-O₂ fuel cell = 1.23 V and ΔH=-285.8 kJ mol^-1
ΔG = -n x F x E°_cell = -2 x 96500 x 1.23
= -237390 J mol^-1
= -237.390 kJ mol^-1
Efficiency = ΔG/ΔH x 100
= -237.390/-285.8 x 100
= 83%.

9. Which of the following statements regarding fuel cells is false?
a) Because of continuous supply, fuel cells never become dead
b) They do not cause pollution
c) Fuel cells have 100% efficiency practically
d) The cost of catalysts needed for the electrode reactions is high
Answer: c
Clarification: Theoretically, the fuel cells are expected to have an efficiency of 100%. However, practically they give efficiency of 60-70%. Still, they are much superior to the thermal power plants in which fuels are burnt to produce heat which then changes water into steam to run the turbine. Such a power plant does not have an efficiency of more than 40%.

10. Which of the following are the common ways to produce H₂ gas in a fuel cell?
a) Coal and biomass gasification
b) Electrolysis and absorption
c) Steam reforming and electrolysis
d) Electromagnetism and steam reforming
Answer: c
Clarification: Since hydrogen does not exist as a gas on Earth, it must be separated from other elements. Hydrogen atoms can be separated from water, natural gas molecules or biomass. The two most common ways to produce hydrogen are steam reforming (using high-temperature steam to produce hydrogen from natural gas) and electrolysis (splitting water).

Chemistry Aptitude Test for Schools on “Extraction of Crude Metal from Concentrated Ore”.

1. What is the type of metallurgy in which the ore is leached and the metal is collected by using electrolysis?
a) Zone refining
b) Hydrometallurgy
c) Liquation
d) Thermite process
Answer: b
Clarification: Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials.

2. A metal found in a free state is called nugget.
a) True
b) False
Answer: a
Clarification: The statement is true. For example, we will take gold in this case, it’s a transition element and it is one of the least reactive chemical elements and is solid under standard conditions. So it exists in free elemental form as nuggets.

3. When is the ore subjected to leach?
a) When the ore is in immiscible liquid
b) When the impurity is in immiscible liquid
c) When both ore and impurity are insoluble in water
d) When only impurity is soluble in water
Answer: c
Clarification: The ore is subjected to leaching when both the ore and impurity are insoluble in water. Leaching process is commonly referred to as extraction. This is a process in which water soluble substances are washed out from soil or wastes.

4. Which of the following statements is wrong?
a) During smelting, flux is used to remove gangue as slag
b) The slag formed during smelting has low melting point and is heavier than metal
c) Calcination of ore is carried out without the presence the oxygen
d) Roasting is carried out in the presence of oxygen
Answer: b
Clarification: Smelting is the process of extraction of a metal from its oxide by reduction with carbon (coke). Alkali metals, alkaline earth metals, etc. cannot be prepared by reduction of their respective oxides with carbon. The slag formed during smelting has high melting point and is lighter than the metal.

5. Roasting results in the formation of oxides. But why are oxide ores are subjected to roasting?
a) To avoid gangue particles
b) To get crude metal with using oxidizing agent
c) To remove volatile impurities in the form of their oxides
d) To make the ore porous
Answer: c
Clarification: Oxide ores are subjected to roasting to remove the volatile impurities in the form of their oxides. It is easier to obtain metals from their oxides (by reduction) than from carbonates or sulphides. So before reduction can be done, the ore is converted into metal oxide.

6. Which of the following ores are concentrated by froth flotation?
a) Haematite
b) Zinc
c) Copper pyrites
d) Magnetite

Answer: c
Clarification: The froth flotation method is widely used for the concentration of sulphide ores such as zinc blende (ZnS), copper pyrites (CuFeS₂), galena (PbS), etc. This method is based upon the fact that the surface of the sulphide ores is preferentially wetted by oils while that of gangue is preferentially wetted by water.

7. Copper is extracted from low grade copper ores.
a) True
b) False
Answer: a
Clarification: The statement is true. Copper is extracted by hydrometallurgy from low grade copper ores. It is leached out using acid or bacteria.The conversion of copper consists of a series of physical and electrochemical processes. The solution containing Cu²⁺ is treated with scrap iron, zinc or hydrogen.

8. What is the main reaction occurring in the blast furnace during extraction of iron from haematite?
a) Fe₂O₃ + 3CO → 2Fe + 3CO₂
b) FeO + SiO₂ → FeSiO₂
c) Fe₂O₃ + 3C → 2Fe + 3CO
d) Fe₂O₃ + CO₂ → FeCO₃ + O₂
Answer: a
Clarification: The main reaction occurring in the blast furnace during extraction of iron from haematite is:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
This reaction involves the reduction of iron (III) oxide to iron and oxidation of carbon monoxide to carbon dioxide.

9. How is ore-dressing of iron done?
a) Froth Flotation
b) Magnetic separation
c) Hand picking
d) By wetting
Answer: b
Clarification: In magnetic separators, the effect of magnetism is used to separate ferromagnetic materials from non-magnetic materials. In principle, this process is also suitable for the iron ores siderite and hematite, which become weakly magnetic when heated.

10. Which of the following metals is not extracted by electrolysis?
a) Na
b) Mg
c) Al
d) Fe
View Answer

Answer: d
Clarification: Actually the extraction of a metal from its ore depends upon the selection of a proper reducing agent. Iron is a moderately active metal and its oxides can be reduced using carbon and not by using electrolysis. Reactive metals, such as aluminium, are extracted by electrolysis, while a less reactive metal, such as iron, may be extracted by reduction with carbon.

Chemistry Aptitude Test for Schools,

Chemistry Multiple Choice Questions on “P-Block Elements – Dioxygen”.

1. Which of the following is the most abundant non-metal in the Earth’s crust?
a) Oxygen
b) Silicon
c) Hydrogen
d) Water

Answer: a
Clarification: Oxygen constitutes about 46-47% of the Earth’s crust, followed by Silicon at 27-28%. Oxygen is predominantly present as a gas in air and several metallic compounds that constitute a metal ore (in the form of oxides). Apart from these, Aluminum is the most abundant metal in the Earth’s crust followed by Iron.

2. What is the source of obtaining oxygen industrially?
a) Metallic ores
b) Air
c) Oxygen furnace
d) Organic compounds
Answer: b
Clarification: Industrially, oxygen is isolated by implying the technique of fractional distillation of liquefied air. Prior to the main operation, air is cleared and filtered off to remove impurities such as carbon dioxide and water vapor. Oxygen distills off as a liquid at -183°C.

3. What is the most stable oxidation state of the oxygen atom?
a) +1
b) -1
c) -2
d) +2
Answer: c
Clarification: Oxygen atom is the most stable in its -2 oxidation state. Here, it gains 2e^– to complete its octet and obtain the noble gas configuration of [Ne]. Rarely does oxygen show +1 and -1 oxidation states. The -1 state is displayed in peroxides. E.g. H₂O₂. It shows +1 in oxygen (I) fluoride, OF₂.

4. Why does aluminum not degrade in nature quickly?
a) It reacts at low temperature
b) It has an octet configuration
c) It has a tough oxide layer
d) It is an electronegative element
Answer: c
Clarification: Aluminum is a passive metal. Meaning, when formed in nature, it quickly reacts with oxygen in the air to form a tough, non-corrosive oxide layer. This layer prevents aluminum metal from reacting with any other substance.

5. Marine life is more comfortable in warm water than cold water. True or false?
a) True
b) False
Answer: b
Clarification: The solubility of gases in a liquid is governed by Henry’s law. It states that the partial pressure of a gas in a solution varies directly. In warmer conditions, the gas particles tend to escape from the water body leading to a lesser amount of dissolved oxygen required for comfortable aquatic conditions.

6. Which of the following in air, forms compounds readily?
a) Nitrogen
b) Oxygen
c) Sulfur
d) Carbon
Answer: b
Clarification: Oxygen, being a highly electronegative element and reactive tends to react with several substances. These include hydrogen and different occurring metals which form compounds. E.g. iron, magnesium, calcium. Nitrogen is highly unreactive since it bears a triple bond and reacts only at high temperatures. Carbon and sulfur are not elements present in air since they are not gases.

7. What will be the products of the reaction – C₂H₄ + 2O₂ →?
a) CO and H₂O
b) CO₂ and H₂O₂
c) Co and H₂O
d) CO₂ and H₂O
Answer: d
Clarification: The reaction show depicts the combustion of ethane. When a hydrocarbon is burned in excess oxygen it forms carbon dioxide and water. Co represents cobalt and CO represents carbon monoxide.

8. What is the nature of zinc oxide?
a) Acidic
b) Amphoteric
c) Basic
d) Undetermined
Answer: b
Clarification: Amphoteric oxides are those oxides which can act both as an acid as well as base. Factually it is determined that zinc, aluminum and tin oxides are amphoteric in nature.

9. Which is the most electronegative atom amongst the following?
a) Oxygen
b) Fluorine
c) Nitrogen
d) Chlorine
Answer: b
Clarification: Accounting for only one missing electron, fluorine is highly reactive. Since it needs only one electron to complete its octet, it is the most electronegative element in the periodic table. The decreasing order of electronegativity is F > Cl > O > N.

10. What happens when an atom of oxygen is subjected to external magnetic field?
a) It is weakly attracted and loses magnetism on removal of field
b) It is weakly attracted and does not lose magnetism on removal of field
c) It is weakly attracted and domains align themselves in the direction of field
d) It is not attracted
Answer: a
Clarification: Oxygen atom is paramagnetic in nature. Meaning, on the application of an external magnetic field, it is slight attracted and loses magnetism on the removal of the field.

Chemistry MCQs for Class 12 on “D and F-Block Elements – Transition Elements Compounds”.

1. What is the colour of KMnO₄?
a) Green
b) Purple
c) Blue
d) Colourless
Answer: b
Clarification: The physical state of potassium permanganate (KMnO₄) is an odourless solid, and they look like dark purple or bronze-coloured crystals. If we dissolve these crystals in water, then the solution becomes purple in colour.

2. What is the formula of hematite?
a) Fe₃O₄
b) FeSO₄.7H₂O
c) Fe₂O₃
d) FeCl₃
Answer: c
Clarification: Ferric oxide(Fe₂O₃) occurs in nature as haematite. It is a red powder, insoluble in H₂O and not acted upon by air or H₂O. It is amphoteric in nature and reacts with acids and alkalis and used as a catalyst in the oxidation of CO to CO₂ in the Bosch process.

3. Mn has a maximum oxidation state of +6.
a) True
b) False
Answer: b
Clarification: The highest oxidation state in the oxides of any transition metal is equal to its group number, for example, 7 in Mn₂O₇. Beyond group 7, no higher oxides of iron above Fe₂O₃ are known. Some metals in higher oxidation state stabilize by forming oxocations.

4. Which of the following is amphoteric?
a) CrO
b) Cr₂O₃
c) CrO₅
d) CrO₃
Answer: b
Clarification: Chromium(atomic no.24, symbol-Cr) forms many oxides. Some of its common oxidation states are +2, +3 and +6. Chromium (III) oxide (green in colour) is amphoteric, i.e., it can react as both acid and base. Its formula is Cr₂O₃.

5. Which of the following is Baeyer’sreagent?
a) Acidified KMnO₄
b) Alkaline KMnO₄
c) Acidified K₂Cr₂O₇
d) Aqueous KMnO₄
Answer: b
Clarification: Alkaline KMnO₄ is called Baeyer’s reagent. Baeyer’s reagent is an alkaline solution of cold potassium permanganate, which is a powerful oxidant making this a redox reaction. Reaction with double or triple bonds (-C=C- or -C≡C-) in an organic material causes the colour to fade from purplish-pink to brown. It is a syn addition reaction.

6. Sc³⁺ is a paramagnetic ion.
a) True
b) False
Answer: b
Clarification: Scandium (atomic no.21, symbol-Sc) has the following electronic configuration:
[Ar] 3d¹4s²
In its Sc³⁺ state, scandium loses the 4s and 3d electrons and is colourless. Hence, Sc³⁺ is diamagnetic and not paramagnetic.

7. Which of the following metal is used as a thermometric liquid?
a) Iron
b) Copper
c) Mercury
d) Potassium
Answer: c
Clarification: Mercury (atomic no.80, symbol-Hg) is the only liquid metal at room temperature. It has a high coefficient of expansion and boiling point. This helps us to identify even the slightest change in temperature of the surroundings.

8. Which of the following tests does AgCl not answer?
a) Chromyl chloride test
b) Baeyer’s reagent test
c) Alkaline test
d) Acidic test
Answer: a
Clarification: Chromyl chloride test is done for detecting the presence of Cl^– ions. The chlorides of silver, lead, mercury and antimony are covalent in nature and thus do not generate Cl^– ions and so they do not give the chromyl chloride test also. So, heavy metal chlorides don’t give this test because they are not ionic.

9. Which compound forms double salt with sulphates of alkali metals?
a) Ferric oxide
b) Silver nitrate
c) Ferric chloride
d) Ferrous sulphate
Answer: d
Clarification: Ferrous sulphate forms double salts with sulphates of alkali metals with general formula R₂SO₄.FeSO₄.6H₂O. With ammonium sulphate, it forms a double salt known as Mohr’s salt. It ionises in solution to gives Fe²⁺, NH₄⁺ and SO₄^2- ions.

10. Which compound is used in Ultra-violet calibration?
a) Hg₂Cl₂
b) HgCl₂
c) K₂Cr₂O₇
d) KMnO₄
Answer: c
Clarification: Potassium dichromate (K₂Cr₂O₇) is especially useful in the visible range but also useful in UV. Potassium dichromate itself is stable and available in high purity. In dilute perchloric acid solution, it has a linear response with good temperature stability and also stable as solution.

Chemistry MCQs for Class 12,

Chemistry Multiple Choice Questions on “Haloalkanes Classification”.

1. Monohalo, dihalo, trihalo and tetrahalo are types of haloalkanes and haloarenes based on the ______
a) type of halogen atom
b) number of halogen atoms
c) nature of carbon atom
d) hybridisation of C atom to which halogen is bonded
Answer: b
Clarification: Haloalkanes may be classified as mono, di, tri, tetra and so on depending on the number of halogen atoms present in their structure.

2. A monohaloarene is an example of a/an __________
a) aliphatic halogen compound
b) aromatic halogen compound
c) alkyl halide
d) side chain substituted aryl halide
Answer: b
Clarification: A monohaloarene is a compound in which the halogen is directly attached to the benzene ring. Side chain substituted aryl halides are also aromatic halogen compounds with the halogen not directly attached to the benzene ring.

3. What is the general formula for haloalkanes? (X=halogen atom, n = 1, 2, 3…)
a) C_nH_2nX
b) C_nH_2n+1X
c) C_nH_2n-1X
d) C_nH_2n-3X
Answer: b
Clarification: The general formula for haloalkanes is C_nH_2n+1X where X is a halogen atom and n = 1, 2, 3… The formulae C_nH_2n-1X and C_nH_2n-3X are that of haloalkenes and haloalkynes respectively.

4. Which of the following compounds contains an allylic carbon?

a) A
b) B
c) C
d) D
Answer: a
Clarification: A sp³ hybridised C atom present adjacent to a C-C double bond is called an allylic carbon, and when the halogen atom is bonded to this carbon, it is called an allylic halide.

5. Which of the following categories does the compound shown belong to?

a) Primary haloalkane
b) Secondary haloalkane
c) Tertiary haloalkane
d) Haloarene
Answer: b
Clarification: The compound shown is cyclohexyl iodide, in which the halogen atom is bonded to an alkyl group that is alicyclic in nature. Since there are effectively two alkyl groups attached to the carbon bonded to the halogen atom, it is classified as secondary or 2° cyclo alkyl halide.

6. What is the nature of the circled C atom in the following compound?

a) sp² hybridised
b) allylic
c) benzylic
d) vinylic
Answer: c
Clarification: The circled C atom is sp³ hybridised and is attached directly to an aromatic ring, hence it is a benzylic carbon and the compound is a 1o benzylic halide.

7. In which of the following cases will the compound be a tertiary (3°) halogen compound? (X=halogen atom)

a) R’=R”=H
b) R’=CH₃, R”=H
c) R’=H, R”=CH₃
d) R’=R”=CH₃
Answer: d
Clarification: When R and R’ both are CH₃ groups, then the carbon atom bonded to the halogen will have three alkyl groups attached to it including the benzene ring.

8. Which of the following is a vinylic halide?
a) CH₂=CHCHCl₂
b) CH₃CHClCH₃
c) (CH₃)₂C=CHCH₂Cl
d) CH₃CH=CClCH₂CH₃
Answer: d
Clarification: In CH₃CH=CClCH₂CH₃, the Cl is bonded directly to the C atom of a C-C double bond, and hence it is a vinylic halide. CH₃CHClCH₃ is an alkyl halide whereas CH₂=CHCHCl₂ and (CH₃)₂C=CHCH₂Cl are allylic halides.

9. The compound C6H5F is an example of a ________ halide.
a) allylic
b) benzylic
c) vinylic
d) aryl
Answer: d
Clarification: In C₆H₅F, the F atom is directly attached to the sp² hybridised carbon atom of an aromatic ring, i.e., benzene.

10. The compound in which a CH₂Br group is attached to a benzene ring is an aryl halide.
a) True
b) False
Answer: b
Clarification: The Br atom is bonded to a carbon atom which is attached to sp² hybridised carbon of benzene. This is an example of a side chain substituted aryl halide.