Question

Assertion (A): The half-life of a reaction is the time in which the concentration of the reactant is reduced to one-half of its initial concentration.

Reason (R): In a first-order reaction, when the concentration of the reactant is doubled, its half-life is doubled.
a) Both A and R are true, and R is the correct explanation of A.
b) Both A and R are true, but R is not the correct explanation of A.
c) A is true, but R is false.
d) A is false, but R is true.

Answer 1

The half-life of a reaction is the time required for a reactant's concentration to decrease to half of its initial value, which is correct. However, for first-order reactions, the half-life is a constant and does not change when the concentration is doubled. Thus, the correct answer is that A is true but R is false.

Step-by-step explanation:

Assertion (A) is correct: The half-life of a reaction is indeed the period of time it takes for the concentration of a reactant to decrease to one-half its initial value.

However, Reason (R) is incorrect: For a first-order reaction, the half-life is constant and does not depend on the concentration of the reactants. Thus, doubling the concentration of the reactant does not double the half-life. The half-life of a first-order reaction is given by the formula t₁/₂ = 0.693/k, where k is the rate constant of the reaction.

The correct answer to the statement given by the student is: A is true, but R is false, making the option (c) the right choice.