Question

An open container has net 10 gm mass of a radioactive material. The net mass in the container after two mean lives is approximately:

• A. 1.35 gm
• B. 2.5 gm
• C. 10 gm
• D. 5 gm

Answer 1

The correct option is A 1.35 gm

A

We have $N=N_o{e}^{-\lambda t}$

Where $\lambda$ = rate constant and

$t$= time

Here $t$ = 2 mean lives $=\frac{2}{\lambda }$

$N=10e^{-2}$ = 1.35gm