Category: Class 11 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Classical Idea of Redox Reactions-Oxidation and Reduction Reactions”.

1. In the reaction of formation of magnesium oxide magnesium undergoes ________
a) reduction
b) oxidation
c) hydrogenation
d) decomposition
Answer: b
Clarification: Oxidation is a process that involves the addition of oxygen to an element or compound or the removal of hydrogen from a compound, an example is of this is the formation of magnesium oxide from magnesium.

2. A zinc ion is formed due to oxidation.
a) true
b) false
Answer: a
Clarification: Oxidation is the loss of electrons by an atom, ion or molecule. it is also known as de^–electronation. Zn → Zn²⁺ + 2e^–, the loss of electrons from zinc i.e. formation of zinc is an example of oxidation.

3. Removal of oxygen from a compound is an example of ________
a) oxidation
b) reduction
c) oxygenation
d) dehydrogenation
Answer: b
Clarification: Reduction is a chemical process, which involves the addition of hydrogen or an element or compound for the removal of oxygen from a compound. An example of reduction is a chemical reaction;
H₂ + F₂ → 2HF.

4. Reduction involves in __________ oxidation number.
a) decrease
b) increase
c) independence
d) remain constant
Answer: a
Clarification: The oxidation number is recharged in which an atom appears to have when all the atoms are removed from it as ions. It may have +ve or -ve sign. Reduction results in a decrease in the oxidation number.

5. Formation of copper from copper iron is an example of a reduction.
a) true
b) false
Answer: a
Clarification: Reduction is the gain of electrons by an atom, ion or molecule this process is known as electronation. Prayer for the formation of copper from copper iron as an example of reduction reaction because the copper gains two electrons in this case.

6. Oxidation is the same as __________
a) addition of hydrogen
b) removal of oxygen
c) addition of oxygen
d) removal of Nitrogen
Answer: c
Clarification: Oxidation is the same as the addition of oxygen or removal of hydrogen where reduction is the addition of hydrogen or removal of oxygen. Oxidation is caused by an oxidising agent and reduction is caused by a reducing agent.

7. Formation of zinc sulphide is an example of ___________
a) reduction
b) oxidation
c) removal of oxygen
d) addition of hydrogen
Answer: b
Clarification: Addition of electronegative element or removal of any other electropositive element is also considered as a process that involves oxidation. Here, sulphur is an electronegative element. So the formation of zinc sulphide is an Oxidation reaction.

8. SnCl₂ + 2FeCl₂ → SnCl₄ + 2FeCl₂ is an example of __________________ reaction.
a) only oxidation
b) only reduction
c) redox
d) neither oxidation nor reduction
Answer: c
Clarification: Chemical reactions which involves both oxygen as well as reduction process simultaneously are known as redox reactions. The above given reaction involves both oxidation and reduction reactions, so it is a Redox reaction.

9. SnCl₂ + 2FeCl₂ → SnCl₄ + 2FeCl₂. Which of the following element undergoes oxidation in the reaction given?
a) iron
b) tin
c) chlorine
d) ferrous
Answer: b
Clarification: Tin changes is oxidation state from + 2 to + 4. Increase in oxidation number indicates Oxidation reaction. Oxidation is the loss of electrons by an atom, ion or molecule, it is also known as the de^–electronation.

10. Which of the following do you think is a correct statement?
a) oxidation is caused by a reducing agent
b) the oxidation reaction is a Redox reaction
c) addition of electropositive element is a type of oxidation
d) reduction is the addition of hydrogen
Answer: d
Clarification: Oxidation is caused by an oxidizing agent, both oxidation and reduction reaction is combined together to form a Redox reaction and the addition of electropositive element is a type of reduction so the correct statement is that reduction as the addition of hydrogen.

Chemistry Multiple Choice Questions on “s-Block Elements – Important Compounds of Calcium”.

1. Which of the following acid chemical formula first slaked lime?
a) Calcium chloride
b) Calcium oxide
c) Calcium hydroxide
d) Calcium carbonate
Answer: c
Clarification: When 1 mole of burnt lime, that is calcium oxide is combined with 1 mole of the hydrogen molecule, a hissing sound appears and slaked lime is produced along with the heat. The chemical formula for slaked lime Ca(OH)₂.

2. Quicklime as same as calcium oxide.
a) True
b) False
Answer: a
Clarification: Yes, calcium oxide chemical formula is CaO and it is also called as quicklime or simply lime. It is prepared by the thermal decomposition of calcium carbonate at 1072-1270 Kelvin, carbon dioxide comes as a byproduct and it is a basic oxide.

3. Which of the following is not a compound of mortar?
a) Phenol
b) Quicklime
c) Sand
d) Water
Answer: a
Clarification: Quicklime or calcium oxide (CaO) is used as a basic flux, for removing the hardness of water, also used in mortar. A mixture of quick lime and sand in the ratio 1:3 with enough water to make a thick place is called motor.

4. What is the enthalpy of heat for dissolving quicklime and water?
a) 55 kJ/mol
b) 63 kJ/mol
c) 75 kJ/mol
d) 78 kJ/mol
Answer: b
Clarification: Calcium hydroxide is prepared by dissolving quicklime and water and the enthalpy change for this reaction is 63 kJ/mole (the sign is negative). Here the chemical formulae for quicklime and Calcium hydroxide are CaO and Ca(OH)₂ has twice respectively.

5. Which of the following compound is formed when slaked lime is treated with excess dioxide in the presence of water?
a) Barium sulphate
b) Calcium carbonate
c) Calcium hydroxide
d) Calcium bicarbonate
Answer: d
Clarification: When 1 mole of Calcium Hydroxide is treated with an excess of carbon dioxide in the presence of water, it results in the formation of calcium bicarbonate which is soluble. It is one of the most important properties of slaked lime.

6. Limestone is insoluble in water.
a) True
b) False
Answer: a
Clarification: Calcium carbonate is also known as limestone or marble are chalk, its chemical formula is given by CaCO₃. It is insoluble in water but dissolves in the presence of carbon dioxide due to the formation of calcium bicarbonate.

7. Can limestone be prepared through slaked lime?
a) Yes
b) No
c) Maybe
d) Cannot say
Answer: a
Clarification: Yes, limestone can be prepared through slaked lime. Limestone is calcium carbonate while slaked lime is calcium hydroxide. When limestone is passed through carbon dioxide, it results in the formation of calcium carbonate which is a precipitate and water.

8. Which of the following do you think is the correct formula for gypsum?
a) CaSO₄.2H₂O
b) CaSO₄.1/2H₂O
c) CaSO₄.H₂O
d) CaSO₄
Answer: a
Clarification: Gypsum is a compound of calcium. It is chemically calcium sulphate dehydrate and it is also known as alabaster. It is added to cement to slow down at speed of setting. It’s really very essential in our day to day life.

9. Gypsum is the same as plaster of Paris.
a) True
b) False
Answer: b
Clarification: Plaster of Paris is calcium sulphate hemihydrate and gypsum is calcium sulphate dihydrate. On heating gypsum at 390 Kelvin, it gives plaster of Paris. The chemical formula of gypsum and plaster of Paris is CaSO₄.2H₂O and CaSO₄.1/2H₂O respectively.

10. What is dead burnt plaster?
a) Hexahydrate calcium sulphate
b) Hemihydrate calcium sulphate
c) Anhydrous calcium sulphate
d) Decahydrate calcium sulphate
Answer: c
Clarification: When plaster of Paris or calcium sulphate hemihydrate, which is given by the chemical formula CaSO₄.1/2H₂O is heated about 393 Kelvin, no water of crystallization is left and anhydrous calcium sulphate is formed, it is known as dead burnt plaster.

11. Is the plaster of Paris useful in setting a solid mass?
a) Yes
b) No
c) Maybe
d) Cannot say
Answer: a
Clarification: When plaster of Paris or calcium sulphate hemihydrate which is given by the chemical formula CaSO₄.1/2H₂O is mixed with water, it forms of plastic mass which sets into a solid mass with slight expansion due to dehydration and its reverse conversion into gypsum.

12. What is chloride of lime?
a) Calcium sulphate
b) Calcium chloro hypochlorite
c) Calcium chloride
d) Calcium hydroxide
Answer: b
Clarification: Chloride of lime is chemically known as calcium chloro hypochlorite and it is given by the chemical formula CaOCl₂, it is also known as bleaching powder. Bleaching powder is prepared by the fusion of calcium hydroxide and chlorine.

13. What is the average percentage of available chlorine theoretically?
a) 85
b) 49
c) 58
d) 66
Answer: b
Clarification: With an excess of dilute sulfuric acid and carbon dioxide, calcium chloro hypochlorite forms chlorine, which is known as available chlorine. The average percentage of available chlorine is 35 to 40% but theoretically, it should be 49%, which diminishes on keeping the Powder due to a chemical change.

14. Which of the following is not a use of calcium chloro hypochlorite?
a) Sterilization of water
b) Manufacture of chloroform
c) Germicide
d) Painting
Answer: d
Clarification: Calcium chloro hypochlorite or chloride of lime or bleaching powder which is chemically CaOCl₂ is used for bleaching, as a disinfectant and germicide in the sterilization of water, for making wool which is unshrinkable and in the manufacture of chloroform.

15. In the average composition of portland cement, the percentage of magnesium oxide is a ___________
a) 3 to 4%
b) 2 to 3%
c) 4 to 5%
d) 1 to 2%
Answer: b
Clarification: Cement is an important building material. The average composition of portland cement is calcium oxide of 50 to 60%, Silicon dioxide of 20 to 25%, aluminium oxide of 5 to 10%, magnesium oxide of 2 to 3%, ferric oxide of 1 to 2% and sulphur trioxide of 1 to 2%.

Chemistry Multiple Choice Questions on “Dalton’s Atomic Theory”.

1. According to Dalton’s Atomic Theory, matter consists of indivisible _______
a) Molecules
b) Atoms
c) Ions
d) Mixtures
Answer: b
Clarification: Atom is the basic unit of life. A molecule is a compound made up of 2 or more atoms held by chemical bonds. The mixture is a combination of pure substances in a ratio. Ion is either positively or negatively charged.

2. Atoms of different elements differ in mass.
a) True
b) False
Answer: a
Clarification: Each and every element has a different mass. For example, carbon’s molecular weight is 12.0107 u, oxygen’s molecular weight is 15.999 u and nitrogen’s molecular weight is 14.0067 u. Hence it’s different for different elements.

3. What did Dalton’s Theory couldn’t explain?
a) gaseous volumes
b) conservation of mass
c) chemical philosophy
d) indivisible atoms
Answer: a
Clarification: Dalton’s atomic theory couldn’t explain gaseous volumes, because as per his view, different elements have different mass but this isn’t true. This is explained by Gay lussac’s law. This is one of the major limitations of Dalton’s atomic theory.

4. What is the name of Dalton’s publication?
a) A New system of atomic Philosophy
b) An old system of Chemical Philosophy
c) A New System of Chemical Philosophy
d) A New System of Chemical Prophecy
Answer: c
Clarification: Dalton published ” A New System of Chemical Philosophy” in 1808. He proposed a theory in that, that is Dalton’s atomic theory. It also has some limitations like it couldn’t explain how molecules combine i.e. their driving force.

5. Which of the following may not be explained by Dalton’s atomic theory?
a) reason for combining atoms
b) conservation of mass
c) chemical philosophy
d) indivisible atoms
Answer: a
Clarification: Dalton’s atomic theory couldn’t explain the reason for combining atoms. This is one of the major limitations of Dalton’s atomic theory. Though it could explain the conservation of mass, indivisible atoms and definite proportions.

6. Law of conservation of mass isn’t explained in Dalton’s atomic theory.
a) True
b) False
Answer: b
Clarification: Law of conservation of mass is explained in Dalton’s atomic theory. He said that reorganization of atoms is involved in chemical reactions. This means mass is neither created nor destroyed in a chemical reaction i.e. explained.

7. What is 1 Dalton?
a) a unified mass unit, 1.360539040(20)×10⁻²⁷kg
b) a unified mass unit, 1.640539040(20)×10⁻²⁷kg
c) a unified mass unit, 1.660539040(20)×10⁻²⁷kg
d) a unified mass unit, 1.660539040(20)×10⁻²⁷kg
Answer: d
Clarification: Dalton is also known as the unified mass unit that is equal to 1.660539040(20)×10⁻²⁷kg or 931.4940954(57)MeV/c² or 1822.888486192(53)m_e (symbol: u, or Da or AMU). It’s a standard unit of mass on the molecular and atomic scale.

8. Could Dalton’s atomic theory explain the laws of chemical combinations?
a) No
b) Yes
c) Only a few
d) Except one
Answer: b
Clarification: Yes, it could explain all the laws of chemical combinations i.e. Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple Proportions, Gay Lussac’s Law of Gaseous Volumes, and Avogadro’s Law.

9. They are no limitations to Dalton’s atomic theory.
a) True
b) False
Answer: b
Clarification: There are limitations to Dalton’s atomic theory. Dalton’s atomic theory couldn’t explain the reason for combining atoms. He also couldn’t explain gaseous volumes, because as per his view, different elements have different mass but this isn’t true. This is explained by Gay lussac’s law.

10. All atoms of a given element have identical __________ including identical _________
a) Properties, mass
b) Weight, volume
c) Volume, properties
d) Temperature, pressure
Answer: a
Clarification: According to Dalton’s Atomic Theory, All atoms of a given element have identical properties, including identical mass. The reason behind this is that they belong to the same element (here “they” is about atoms).

Chemistry Multiple Choice Questions on “Periodic Trends in Properties of Elements”.

1. Atomic radii ____________ along the periods.
a) Increases
b) Decreases
c) Remains constant
d) Irregular
Answer: b
Clarification: Atomic radii decreases along the periods because as the number of electrons increases in the same shell of the atom, the effective nuclear attraction increases, thereby reducing the distance between the outer shell and the nucleus i.e. decreasing atomic radii.

2. O^2-, F^–, Na⁺ and Mg²⁺ are called as __________
a) Isoelectronic species
b) Isoneutral species
c) Isotopes
d) Isobars
Answer: a
Clarification: O^2-, F^–, Na⁺ and Mg²⁺ are known as isoelectronic species as they all have the same no. of electrons(10). Isotopes contain the same no. of protons but a different number of neutrons. Isobars have the same mass number but a different atomic number.

3. X_(g) → X⁺_(g) + e^–. What does this chemical reaction need to occur?
a) Catalyst
b) Electron affinity
c) Electropositivity
d) Ionization energy
Answer: d
Clarification: The minimum amount of energy that is required to remove an electron from an atom is called Ionization enthalpy. It is expressed in the units KJ/mol. Electron affinity is the change in the energy when we add an electron to a neutral atom. Electropositivity is a metallic characteristic. A catalyst speeds up the reaction.

4. What is the correct order of electronegativity among the following options?
a) Lib) Lic) Li>Na>K>Cs>Rb
d) Li>Na>K=Rb>Cs
Answer: d
Clarification: Electronegativity is the measure of the ability to attract shared electrons to itself of an atom in a chemical compound. The values of electronegativities of Li, Na, K, Rb and Cs are 1, 0.9, 0.8, 0.8 and 0.7 respectively.

5. Ionization energies are always positive.
a) True
b) False
Answer: a
Clarification: As the ionization energy is the minimum amount of energy that is required to remove an electron from an atom. As the energy is always needed for the removal of an electron from an atom, the values of ionization energies are always positive.

6. What is the oxidation state of Mn in KMnO₄?
a) 5
b) 6
c) 7
d) 4
Answer: c
Clarification: The total charge of the compound KMnO₄ is zero as it is a neutral and stable compound. As we know the oxidation states of K and O are +1 and -2 respectively. So +1 + Mn charge + 4(-2) = 0; Mn charge = 7.

7. The relationship between Li, Mg and Be, Al is called the __________ relationship.
a) Diagonal
b) Periodic
c) Group
d) Triangle
Answer: a
Clarification: The Elements Li and Mg, Be and Al are similar to each other in the case of formation of different compounds in a similar composition. They have a sort of similar behaviour with each other, so they are said to be in a diagonal relationship as per their place in the periodic table.

8. N₂O is a _________
a) Tear gas
b) Laughing gas
c) Acid
d) Base
Answer: c
Clarification: N₂O is called laughing gas as it has euphoric effects after being inhaled. It is one of the World Health Organization’s Essential Medicines. it is used for recreational and anaesthetic purposes mostly.

9. Which of the following is superoxide?
a) K₂O
b) Na₂O
c) MgO
d) KO₂
Answer: d
Clarification: In the superoxide of the element, the oxygen’s oxidation state is given by -1/2. In peroxides, the oxidation state of oxygen is -1 as in case of hydrogen peroxide. The oxygen’s oxidation state in KO₂ is -1/2.

10. What can be tested using a litmus paper?
a) Acidic nature only
b) Basic nature only
c) Both acidic nature and basic nature
d) Nothing
Answer: c
Clarification: A litmus paper is a dye that is extracted from lichens. It used to test acidic nature and basic nature of a substance. Red colour indicates acidic nature and blue colour indicated basic nature. Neutral litmus paper is purple in colour.

Chemistry Multiple Choice Questions on “Thermodynamics – Enthalpies for Different Types of Reactions”.

1. Enthalpy of combustion as always ________
a) positive
b) negative
c) 0
d) infinity
Answer: b
Clarification: Enthalpy of combustion is the enthalpy change that takes place when one mole of a compound undergoes complete combustion in the presence of oxygen. It is represented by ΔHc, it is always negative because the process of combustion is exothermic.

2. Calculate the heat of combustion of ethane, in the reaction C₂H_6(g) + 3 1/2O_2(g) → 2CO_2(g) + 3H₂O_(l) where the heats of formation of ethane gas, carbon dioxide gas and water liquid are –84.7 kJ mol^-1, -393.5 kJ mol^-1 and –285.8 kJ mol^-1 respectively.
a) -1559.7 kJ mol^-1
b) -155.7 kJ mol^-1
c) -159.7 kJ mol^-1
d) -559.7 kJ mol^-1
Answer: a
Clarification: Given that C₂H₆(g) + 3 1/2 O_2(g) → 2CO_2(g) + 3H₂O_(l) As we know that, ΔHr = Σ ΔH_f[products] – Σ ΔH_f[reactants]; ΔH_c(C₂H₆) = 2 X (-393.5 kJ mol^-1) + 3 X (-285.8 kJ mol^-1) – (- 84.7 kJ mol^-1) – 2 X (0 kJ mol^-1) = ΔH_c(C₂H₆) = – 1559.7 kJ mol^-1.

3. The enthalpy of 435 KJ per Mol is obtained from the conversion of hydrogen molecule into two hydrogen atoms.
a) True
b) False
Answer: a
Clarification: The enthalpy change that occurs when one mole of a molecule breaks into its atoms is known as enthalpy of atomization. The energy released during the conversion of a hydrogen molecule into two hydrogen atoms is enthalpy of atomization.

4. In which of the following reactions the energy released is not an enthalpy of atomization?
a) decomposition of a hydrogen molecule into two hydrogen atoms
b) decomposition of an oxygen molecule into 2 oxygen atoms
c) formation of a water molecule
d) decomposition of chlorine molecule
Answer: c
Clarification: The enthalpy of atomization is an enthalpy change that occurs when one molecule of a molecule breaks into its atoms, but here the of a water molecule formation does not satisfy the definition of the enthalpy of atomization.

5. In case of the decomposition of hydrogen molecule into two hydrogen atoms, the enthalpy of atomization is same as the _________
a) bond dissociation enthalpy
b) enthalpy of formation
c) enthalpy of combustion
d) enthalpy of sublimation
Answer: a
Clarification: In case of the decomposition of hydrogen molecule the enthalpy is the same as enthalpy of atomization as well as bond dissociation enthalpy because the bond association enthalpy refers to the breakage of H-H Bond. So that two hydrogen atoms are formed whereas enthalpy of atomization is the breakage of hydrogen molecules in order to form two atoms.

6. Calculate the carbon carbon double bond energy in ethane from the following reaction, H₂C=CH₂(g) + H₂(g) –> H₃C−CH₃(g) ΔH = −138 kJ/mol. If Bond enthalpies are: C−C = 348; H−H = 436; C−H = 412 in KJ/mol.
a) 498 KJ/mol
b) 593 KJ/mol
c) 508 KJ/mol
d) 598 KJ/mol
Answer: d
Clarification: By following the rule ΔH_r = Σ ΔH_f[products] – ∑ ΔH_f[reactants], we get -(x + 4(412) + 432) + (348 + 6(412)) = -138 KJ/mol; x = 598 KJ/mol. So the carbon carbon double bond energy in Ethane is given as 598 KJ per Mol.

7. Decomposition of sodium chloride into a sodium ion and chloride ion releases energy of 788 KJ per Mol, what is the energy called?
a) lattice energy
b) translation energy
c) dilution energy
d) neutralization energy
Answer: a
Clarification: Lattice enthalpy is the enthalpy change when one molecule of an ionic compound dissociates into its ions and gaseous state. Here sodium chloride is an ionic compound and it decomposes into sodium and chloride ions, so the energy released is lattice energy.

8. Which of the following cycle allows has to analyze reaction energies?
a) carbon cycle
b) born Haber cycle
c) nitrogen cycle
d) chemical cycle
Answer: b
Clarification: An indirect method, in which we can construct an enthalpy diagram is called a Born-Haber cycle as it is nearly impossible to determine lattice enthalpies directly by experiment. It is an approach to analyze reaction energies.

9. Enthalpy of solution can either be positive or ________
a) negative
b) does not exist
c) 0
d) infinity
Answer: a
Clarification: Enthalpy change when 1 mole of a substance is dissolved in a large excess of solvent so that on further delusion no appreciable heat change occurs, is known as enthalpy of solution. It can either be positive or negative depending on the reaction, whether it is exothermic or endothermic.

10. The enthalpy of dilution of a solution is __________ on the original concentration of the solution and the amount of solvent added.
a) dependent
b) independent
c) may be dependent
d) may be independent
Answer: a
Clarification: Enthalpy of dilution is the enthalpy change when 1 mole of a substance is diluted from one concentration to another. So it is dependent on your original concentration of the solution and the amount of solvent added.