Category: Class 12 Chemistry Objective Questions

Chemistry Quiz for Class 12 on “Collision Theory of Chemical Reactions”.

1. When a catalyst is involved in the collision between the reactant molecules, more energy is required.
a) True
b) False
Answer: b
Clarification: When a catalyst is involved in a collision between the reactant molecules, less energy is required for the chemical reaction to take place. Catalyst brings down the activation energy of the overall chemical reactions and the reaction takes place at a lower energy state.

2. Which of the following explains the increase in the reaction rate by a catalyst?
a) Catalyst decreases the rate of backward reaction so that rate of forward reaction increases
b) Catalyst provides extra energy to reacting molecules so that they produce effective collisions
c) Catalyst provides an alternative path of lower activation energy to the reactants
d) Catalyst increases the number of collisions between the reacting molecules.
Answer: c
Clarification: It is because when the activation energy (E_a) is lower in a reaction, more number of reactant particles have enough energy to react and form products. Hence, it provides an alternative path and the reactions tend to occur faster.

3. Effective collisions are those in which molecules must acquire the energy of activation.
a) True
b) False
Answer: a
Clarification: For the collisions to be effective, molecules must collide with sufficient energy, known as activation energy so that chemical bonds can break. This causes the reaction to occur faster and to form the required products.

4. Who put forward the collision theory of chemical reactions?
a) Trautz and Lewis
b) Luigi Galvani
c) Henry Cavendish
d) Alessandro Volta
Answer: a
Clarification: In 1916, Max Trautz and William Lewis put forward the collision theory giving a better explanation about the rates of reactions. According to this theory, it is assumed that the reactant molecules are hard spheres and reaction between them occurs only when they collide with each other.

5. The proper orientation of reactant molecules leads to bond formation.
a) True
b) False
Answer: a
Clarification: Proper orientation of reactant molecules leads to bond formation because improper orientation makes the reactant molecules bounce back and hence the reaction won’t take place and the required products will not to be formed.

6. Which of the following is a drawback of collision theory?
a) Proper orientation
b) High activation energy
c) Hard spheres
d) Have energy equal to or greater than the threshold energy
Answer: c
Clarification: In Collision theory, activation energy and proper orientation of molecules together determine the criteria for an effective collision but it has a certain drawback as it considers atoms/molecules to be hard spheres and ignores their spherical aspects.

7. What is the term used to refer to the number of collisions per unit volume of the reaction mixture?
a) Collision force
b) Collision frequency
c) Collision energy
d) Collision time period
Answer: b
Clarification: The number of collisions per unit volume of the reaction mixture is known as collision frequency. According to this theory, the reactant molecules are assumed to be hard spheres and reaction is postulated to occur when molecules collide with each other.

8. What is the rate of reaction for a bimolecular elementary reaction?
a) Z_AB e^-E_a/RT
b) Z_AB e^E_a/RT
c) – Z_AB e^-E_a/RT
d) – Z_AB e^E_a/RT

Answer: a
Clarification: The rate of reaction is equal to the product of collision frequency of reactants and the fraction of molecules whose energies are equal to or greater than that of the energy of activation. Where Z_AB represents collision frequency of reactants, A and B and e^-E_a/RT represents a fraction of molecules with energies equal to or greater than E.

9. In a chemical reaction, if the reactant requires a high amount of activation energy, then what is the behaviour of the reaction?
a) Fast
b) Slow
c) Instantaneous
d) Doesn’t depend on activation energy
Answer: b
Clarification: The reaction occurs slowly only if the reactants are slow, so if the reactants are slow we have to provide a high amount of Activation energy (E_a) to the reactants. This enhances the speed of the reactants in the reaction and to form products.

10. What are the factors that determine an effective collision?
a) Translational collision and energy of activation
b) Threshold energy and proper orientation
c) Proper orientation and steric bulk of the molecule
d) Collision frequency, threshold energy and proper orientation
Answer: d
Clarification: The factors that determine an effective collision are:
Collision frequency: The number of collisions per unit volume of the reaction mixture is known as collision frequency.
Threshold energy: Threshold energy is the minimum kinetic energy the molecules must have to bring about effective collisions between two reactant molecules considered as hard spheres, resulting in a chemical reaction. Proper orientation.

Chemistry Quiz for Class 12,

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

1. Which of the following compounds can be used to obtain free nitrogen?
a) NaNO₂
b) HNO₂
c) HNO₃
d) Ba₃N₂
Answer: a
Clarification: NaNO₂, sodium nitriteis the only convenient compound that can be used to obtain free nitrogen, even in laboratories. Sodium nitrite can be reacted with ammonium chloride, both in aqueous form, producing NaCl and nitrogen, N₂ along with water and small traces of HNO₃ and NO.

2. How many stable isotopes does the nitrogen atom have?
a) 16
b) 20
c) 2
d) 3
Answer: c
Clarification: The nitrogen atom has two stable isotopes: ¹⁴N and ¹⁵N, 99.6% and 0.4% (by mass) respectively. There are also fourteen known radioisotopes with one additional nuclear isomer.

3. Nitrogen atom is represented at ¹⁴₇N. How many electrons does it need to attain the noble gas configuration?
a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: With five electrons in its outer most shell, it needs three more electrons to have a complete shell consisting of eight electrons which is the noble electronic configuration. The ion formed by the nitrogen atom is N^3-. It attains the electronic configuration on neon.

4. Why does nitrogen show anomalous properties with respect to other elements in group 15?
a) Nitrogen has low ionization enthalpy
b) Nitrogen atomhas high inter-electronic repulsions
c) Nitrogen molecule bears a triple bond
d) Absence of vacant d-orbitals

Answer: d
Clarification: Nitrogen shows anomalous properties compared to other elements of group 15 because of the absence of vacant d-orbitals. In addition to this, anomalous properties are a result of nitrogen atom’s smaller size, highest electronegativity and highest ionization energy with respect to all the elements in group 15.

5. Why is nitrogen preferably used in welding process and cooling of substances?
a) It’s a gas and can easily be handled
b) It has an extremely low freezing point
c) It is an inert gas
d) It is non-toxic

Answer: c
Clarification: Gases like argon is also nontoxic. However, nitrogen gas is still the most preferred since it eliminates all the possibilities of unwanted oxidation and explosions. In the welding industry this prevents metals from corroding. Nitrogen is used in the food industry for packaging since it provides a pressurized atmosphere that reduces package collapse.

6. Which oxide of nitrogen is released from car engines?
a) Nitrogen dioxide
b) Nitric oxide
c) Nitrous oxide
d) Nitrogen tetroxide
Answer: b
Clarification: Car engines release only nitric oxides. Nitrogen and oxygen from the air combine at high temperatures in the engine to produce nitrogen (II) oxide by the reaction N_2(g) + O_2(g) → 2NO_(g). Nitric oxides rise in the atmosphere and are oxidized to nitrogen dioxide, NO₂ which dissolves in the precipitating water to form acid rain.

7. What is the name of the natural process that is responsible for replenishing N₂ back in the atmosphere from NO₃^–?
a) Nitrification
b) Nitrogen fixation
c) De-nitrification
d) Nitrate fixation
Answer: c
Clarification: All the mentioned steps are critical in the nitrogen cycle. However, de-nitrification is that particular step where microbes in the soil reduce nitrate ions, NO₃^–, to free nitrogen gas, N₂. It also releases few nitrogen oxides as by-products.

8. When liquid nitrogen is poured onto the hand, it slips away without affecting the hand actually. What is this phenomenon called?
a) Kaye effect
b) Kinetic isotope effect
c) Kondo effect
d) Leiden frost effect
Answer: d
Clarification: The Leiden frost effect creates a small layer of insulating vapor layer just at the instant when the liquid particle strikes a surface comparatively a lot hotter than liquid. Liquid nitrogen is at -196°C and the human body at 38°C. This insulating vapor layer prevents the liquid to further come in contact with the body which then slips away.

9. Which group does the name ‘pnictogens’ refer to?
a) Group 11
b) Group 13
c) Group 15
d) Group 14
Answer: c
Clarification: The group 15 of periodic table is better known as the ‘pnicogens’. Pnicogen means ‘to choke’. Since all the elements in this group is choking in nature, including the choking property of nitrogen. Group 11 does not have a specific name; group 13 is referred to as the Boron group. Group 14 is known as the Carbon group.

10. How many allotropes does nitrogen have?
a) Zero
b) One
c) Two
d) Three
View Answer

Answer: a
Clarification: Nitrogen atom does not exhibit allotropy. This is because of its relatively small size and high inter-electronic repulsion due to which the N – N becomes extremely weak. However, theoretically there are two predicted forms of allotropes of nitrogen. First, alpha nitrogen assumes a cubic structure and exists only below 35.6 K which is a whooping -237.55°C. Beta nitrogen exists from 35.6 K to 63.15 K. After that, it melts.

Chemistry Multiple Choice Questions on “P-Block – Group 17 Elements”.

1. Group 17 elements are also called halogens.
a) True
b) False
Answer: a
Clarification: Group 17 elements are called halogens. The name halogen (Greek, halo = sea salts, genes = producing) meaning sea salt formers was given to them by Schweigger in 1811 because the salts (chlorides, bromides and iodides) of the first three elements occur in sea water.

2. Which of the following element is most reactive?
a) Chlorine
b) Fluorine
c) Bromine
d) Iodine
Answer: b
Clarification: Of all the halogens, fluorine is the most reactive and hence is also called super halogen. Fluorine is also the most electronegative (EN = 4.0) element in the periodic table. This indicates that fluorine has a high tendency to gain electrons from other elements with lower electronegativities.

3. Which of the following halogen is radioactive?
a) Fluorine
b) Bromine
c) Astatine
d) Chlorine
Answer: c
Clarification: Astatine (Atomic No. = 85, Symbol-At) is radioactive and hence occurs in nature only in traces. Therefore, not much is known about its chemistry, though it might be expected to be a metalloid.

4. Halogens do not occur in the free state.
a) True
b) False
Answer: a
Clarification: Halogens are highly reactive elements and hence do not occur in the free state or native state. They mainly occur in the combined state in the form of their halide (X^–) salts although iodine also occurs as iodate (IO₃^–).

5. Which of the following is not a mineral of fluorine?
a) Fluorspar
b) Cryolite
c) Fluoroapatite
d) Carnallite
Answer: d
Clarification: Fluorine occurs as insoluble fluorides to the extent of 0.07% in the earth’s crust. The chief minerals of fluorine are:

• Fluorspar, CaF₂
• Cryolite, Na₃AlF₆
• Fluoroapatite, CaF₂.3Ca₃(PO₄)₂