Question

Select One Option Correct from the following :The half-life of the radioactive Radon is 3.8 days. The time, at the end of which 1/20 th of the Radon sample will remain undecayed, is [Given $\log_{10} e = 0.4343.$]
(A) 3.8 days
(B) 16.5 days
(C) 33 days
(D) 76 days

Answer 1

Answer : (b) 16.5days

Explanation :

Equation for decay of radioactive nuclei will be

N=N0e−λt

Where λln2t12=ln238

N020=N0e−ln2.8t

t=16.5days.