Question

The masses of two radioactive substance are same and their half lives are 1 hr and 2yr respectively. The ratio of their activities after 4yr will be:

• A. 1 : 4
• B. 1 : 2
• C. 1 : 3
• D. 1 : 6

Answer 1

The correct option is A

1 : 4

$T=4year$
$t_{\frac{1}{2}}=1year$ $t_{\frac{1}{2}}=2year$
$n=\frac{T}{t_{\frac{1}{2}}}=4$ $n=\frac{4}{2}=2$
$N_1=N_0[\frac{1}{2}{]}^4$ $N_2=N_0[\frac{1}{2}{]}^2$
$\frac{N_1}{N_2}=\frac{1}{4}$