Question

If half-life of a substance is 3.8 days and its quantity is 10.38 gm. Then substance quantity remaining left after 19 days will be.

• A. 0.151 gm
• B. 0.32 gm
• C. 1.51 gm
• D. 0.16 gm

Answer 1

Answer: (B)

0.32 gm

Answer 2

Number of half lives

$n = \frac{19}{3.8} = 5;$ Now $\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{n}$

$\Rightarrow \frac{N}{10.38} = \left( \frac{1}{2} \right)^{5} \Rightarrow N = 10.38 \times \left( \frac{1}{2} \right)^{5} = 0.32gm$