Find out time period of Ist order reaction when reaction complete 2/3rd, if the value of rate constant is 4.3 10 s x (JIPMER 2019) (a) 0.0025 10 sec x (b) 0.25 10 sec x (c) 0.025 10 sec x (d) 2.5 10 sec x

For a first order reaction, 2.303 a t log k a x Where, a = initial concentration a – x final concentration Given, rate constant (k) = 4.3 × 10-4 s-1 Let, the initial concentration = a Final concentration (a – x) 2 a a a 3 3 For first order reaction, 2.303 log a t k a x 4 2.303 log / 3 4.3 10 a a x 3 2.5 10 x sec Thus, option (d) is correct.