Question

half life of a radioactive substance A is 4 days. the probability that a nucleus will decay in two half lives is:

Answer 1

The correct option is C 3/4
$\begin{array}{c}Aftertwohalflives\frac{1^{th}}{4}fractionofnucleiwillremainundecayed\\ or,\frac{3^{th}}{4}fractionwilldecay\\ hencetheprobabilitythatanucleusdecaysintwohalflivesis\frac{3}{4}\end{array}$

Hence,

option $\left(C\right)$ is correct answer.