Important MCQs for CBSE Class 12 Chemistry Board Exam. As we all are aware that Term 1 of CBSE Class 12 board exam 2021-2022 will be based on MCQs in which 50% syllabus will be assessed hence it is very important that students must have an idea about the format and difficulty level of such questions. Some questions are given here and all the questions are available in the PDF provided by CBSE. Link to download the PDF is given at the end of this article.
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CBSE Class 12 Chemistry: Important MCQs
Read the passage given below and answer the following questions:
The rate of a reaction, which may also be called its velocity or speed, can be defined with relation to the concentration of any of the reacting substances, or to that of any product of the reaction. If the species chosen is a reactant which has a concentration c at time t the rate is - dc/dt, while the rate with reference to a product having a concentration x at time t is dx/dt. Any concentration units may be used for expressing the rate; thus, if moles per liter are employed for concentration and seconds for the time, the units for the rate are moles liter-1 sec-1.
For gas reactions pressure units are sometimes used in place of concentrations, so that legitimate units for the rate would be (mm. Hg) sec-1 and atm. sec-1
The order of a reaction concerns the dependence of the rate upon the concentrations of reacting substances; thus, if the rate is found experimentally to be proportional to the α th power of the concentration of one of the reactants A, to the β th power of the concentration of a second reactant B, and so forth, via., rate = k CA α CB β (1)
the overall order of the reaction is simply n = α + β + ----- (2)
Such a reaction is said to be of the αth order with respect to the substance A, the β th order with respect to B and so on...
(Laidler, K. J., & Glasstone, S. (1948).
Rate, order and molecularity in chemical kinetics. Journal of Chemical Education, 25(7), 383.)
In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.
A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statement but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.
1. Assertion: Rate of reaction is a measure of change in concentration of reactant with respect to time. Reason: Rate of reaction is a measure of change in concentration of product with respect to time.
2. Assertion: For a reaction: P +2Q Products, Rate = k [P]1/2[Q]1 so the order of reaction is 1.5 Reason: Order of reaction is the sum of stoichiometric coefficients of the reactants.
3. Assertion: The unit of k is independent of order of reaction. Reason: The unit of k is moles L-1s -1 .
4. Assertion: Reactions can occur at different speeds. Reason: Rate of reaction is also called speed of reaction.
Read the passage given below and answer the following questions:
Adenosine triphosphate (ATP) is the energy-carrying molecule found in the cells of all living
things. ATP captures chemical energy obtained from the breakdown of food molecules and
releases it to fuel other cellular processes. ATP is a nucleotide that consists of three main
structures: the nitrogenous base, adenine; the sugar, ribose; and a chain of
three phosphate groups bound to ribose. The phosphate tail of ATP is the actual power source
which the cell taps. Available energy is contained in the bonds between the phosphates and is
released when they are broken, which occurs through the addition of a water molecule (a
process called hydrolysis). Usually only the outer phosphate is removed from ATP to yield
energy; when this occurs ATP is converted to adenosine diphosphate (ADP), the form of
the nucleotide having only two phosphates.
The importance of ATP (adenosine triphosphate) as the main source of chemical energy in
living matter and its involvement in cellular processes has long been recognized. The primary
mechanism whereby higher organisms, including humans, generate ATP is through
mitochondrial oxidative phosphorylation. For the majority of organs, the main metabolic fuel
is glucose, which in the presence of oxygen undergoes complete combustion to CO2 and H2O:
C6H12O6 + 6O2 → 6O2 + 6H2O + energy
The free energy (ΔG) liberated in this exergonic (ΔG is negative) reaction is partially trapped
as ATP in two consecutive processes: glycolysis (cytosol) and oxidative phosphorylation
(mitochondria). The first produces 2 mol of ATP per mol of glucose, and the second 36 mol
of ATP per mol of glucose. Thus, oxidative phosphorylation yields 17-18 times as much
useful energy in the form of ATP as can be obtained from the same amount of glucose by
The efficiency of glucose metabolism is the ratio of amount of energy produced when 1 mol
of glucose oxidised in cell to the enthalpy of combustion of glucose. The energy lost in the
process is in the form of heat. This heat is responsible for keeping us warm.
(source: Erecińska, M., & Silver, I. A. (1989). ATP and Brain Function. Journal of Cerebral
Blood Flow & Metabolism, 9(1), 2–19. https://doi.org/10.1038/jcbfm.1989.2 and
Q1. Cellular oxidation of glucose is a:
- spontaneous and endothermic process
- non spontaneous and exothermic process
- non spontaneous and endothermic process
- spontaneous and exothermic process
Q2. What is the efficiency of glucose metabolism if 1 mole of glucose gives 38 ATP
energy?(Given: The enthalpy of combustion of glucose is 686 kcal, 1ATP= 7.3kcal)
Q3. Which of the following statement is true?
- ATP is a nucleoside made up of nitrogenous base adenine and ribose sugar .
- ATP consists the nitrogenous base, adenine and the sugar, deoxyribose.
- ATP is a nucleotide which contains a chain of three phosphate groups bound to ribose sugar.
- The nitrogenous base of ATP is the actual power source.
Q4. Nearly 95% of the energy released during cellular respiration is due to:
- glycolysis occurring in cytosol
- oxidative phosphorylation occurring in cytosol
- glycolysis in occurring mitochondria
- oxidative phosphorylation occurring in mitochondria
Q5. Which of the following statements is correct:
- ATP is a nucleotide which has three phosphate groups while ADP is a nucleoside which three phosphate groups.
- ADP contains a nitrogenous bases adenine, ribose sugar and two phosphate groups bound to ribose.
- ADP is the main source of chemical energy in living matter.
- ATP and ADP are nucleosides which differ in number of phosphate groups.
(Answer: 1D, 2B (Glucose catabolism yields a TOTAL of 38 ATP. 38 ATP x 7.3 kcal/mol
ATP = 262 kcal. Glucose has 686 kcal. Thus the efficiency of glucose metabolism is
262/686 x 100 = 38%. ), 3C, 4D, 5B)
Many more similar questions are available in the PDF of the question bank published by CBSE.