Question

Half-life of a substance is 6 min. If its initial amount is 32 g, then amount present after 18 minis:

• A. 4g
• B. 8g
• C. 16g
• D. 2g

Answer 1

Answer: (A)

4g

Answer 2

${{\text{t}}_{1/2}}=6\,\min$
${{N}_{0}}=32\,g$
$\text{Total}\,\text{time}\,\text{=}\,\text{18}\,\text{min}$
$\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}$
$n=\frac{\text{Total}\,\text{time}}{\text{Half}-\text{life}}=\frac{18}{6}3$
$\frac{N}{32}={{\left( \frac{1}{2} \right)}^{3}}$
$\frac{N}{32}=\frac{1}{8}$
$N=\frac{32}{8}=4\,g$