Question

After five half lives percentage of original radioactive atoms left is

• A. $1\%$
• B. $0.3\%$
• C. $3.125\%$
• D. $0.2\%$

Answer 1

Answer: (C)

$N=N_0{\left(\frac{1}{2}\right)}^n$
where $n=5$
$\therefore N=\frac{N_0}{32}$
$N=3.125\%$ of $N_0$