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

(A) 1/4

(B) 3/4

(C) 1/2

(D) 1

Ans: (B)

Sol: $\large N = N_0 (\frac{1}{2})^n$

$\large \frac{N}{N_0} = (\frac{1}{2})^2 = \frac{1}{4}$

Probability of Decay $\large = 1- \frac{N}{N_0}$

$\large = 1- \frac{1}{4} = \frac{3}{4}$