Question

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

• A. $\lambda m$
• B. $\frac{\lambda m}{M}$
• C. $\frac{\lambda m{N}_A}{M}$
• D. $m{N}_A{e}^{\lambda }$

Answer 1

The correct option is C $\frac{\lambda m{N}_A}{M}$

Activity is given by
$A=\lambda M$
where N: no. of nuclei
$M\to N_A$ numbers of nuclei
$m\to N$ numbers of nuclei
$\Rightarrow M=\frac{m{N}_A}{M}$
$\Rightarrow A=\frac{\lambda m{N}_A}{M}$