Question

A sample of radioactive material has mass m, decay constant λ, and molecular weight M. Avogadro constant = N_A. The initial activity of the sample is

(a) λm

(b) λm/M

(c) λm N_A/M

(d) mN_Ae λ

Answer 1

Correct Answer is: (c) λm N_A/M

Activity = number of disintegrations per unit time

= |dN/dt| = λ. N, where N = the total number of nuclei.

Also, N = number of moles x N_A = (m/M) N_A.