Question

A radioactive element has a half life of 200 days. The percentage of original activity remaining after 83 days is ________. (Nearest integer) (Given : antilog 0.125 = 1.333, antilog 0.693 = 4.93)

Answer 1

The correct answer is 75
$λ=\frac{2.303}{t} log\frac{A_0}{A}$
$\frac{0.693}{200}=\frac{2.303}{83}log\frac{A_0}{A}$
$\frac{A}{A_0}=0.75$
Therefore, percentage of original activity remaining after 83 days is 75%.