Question

The half-life of radioactive radon is $3.8$ days. The time at the end of which $\frac{1}{20}th$ of the radon sample will remain undecayed is (given $lo{g}_{10}e=0.4343)$

• A. $3.8$ days
• B. $16.5$ days
• C. $33$ days
• D. $76$ days

Answer 1

The correct option is B $16.5$ days

$N=N_o{e}^{-\lambda t}$
$t_{1/2}=\frac{ln2}{\lambda }$
$\frac{1}{20}=e^{-\frac{ln2}{3.8}t}$
$t=16.5days$