Question

If $N_0$ is the original mass of the substance of half-life period $t_{1/2} = 5 $ years, then the amount of substance left after $15$ years is

• A. $N _{0} / 8$
• B. $N _{0} / 16$
• C. $N _{0} / 2$
• D. $N _{0} / 4$

Answer 1

Answer: (A)

After every half-life, the mass of the substance reduces to half its initial value.
$N_0 \xrightarrow{5 \text { years }}\frac{N_0}{2} \xrightarrow{5 \text { years }}\frac{N_0 / 2}{2}$
$=\frac{N_0}{4} \xrightarrow{5 \text { years }}\frac{N_0 / 4}{2}=\frac{N_0}{8}$