Half life of a first order reaction is 20 minute. The time taken to reduce the initial concentration of reactant to (1 / 10)^ th is

Step-by-step solution

Half-life and first-order reaction kinetics provide the framework for solving this problem. The half-life t_ 1/2 = 20 min yields the rate constant k = 0.693 t_ 1/2 = 0.03465 min ⁻¹ . The integrated rate law k = 2.303 t [A]₀ [A]_t applies when [A]_t = 1 10 [A]₀ , making [A]₀ [A]_t = 10 = 1 . Rearranging gives t = 2.303 k = 2.303 0.03465 66.46 min . The result corresponds to option B: 66.46 min .