Question

10.24 g radioactive substance of half life 3.8 days, than after 19 days, remaining quantity is:-

• A. 0.151 g
• B. 0.32 g
• C. 1.51 g
• D. 0.16 g

Answer 1

The correct option is B 0.32 g

According law of radio activity, $N=N_0{e}^{-\lambda t}$

where $N=$ remaining quantity after decay time $t$, $N_0=$ initial amount of the substance at $t=0$, $\lambda =$ decay constant.

Now, $\lambda =0.693/t_{1/2}=0.693/3.8=0.182$

Thus, $N=10.24e^{-0.182\times 19}=0.32g$