Question

After two hours, one-sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is

• A. 15 minutes
• B. 30 minutes
• C. 45 minutes
• D. 4 hour

Answer 1

Answer: (B)

30 minutes

Answer 2

The correct option is (B): 30 minutes
$N=N_{0}\left(\frac{1}{2}\right)^{n}$
or $\frac{N_{0}}{16}=N_{0}\left(\frac{1}{2}\right)^{n}$
or $n=4$
Halflife $t_{1/2}=\frac{t}{n}=\frac{2}{4}=\frac{1}{2} h$
T=0.5hour=30 minutes.