Question

A substance is kept for 2 hours and three-fourth of that substance disintegrates during this period. The half life of the substance is :

• A. 2 hr
• B. 1 hr
• C. 30 min
• D. 4 hr

Answer 1

Answer: (B)

1 hr

Given,

Amount left N = $1-\frac{3}{4}=\frac{1}{4}$

$N=N_0{\left(\frac{1}{2}\right)}^n\Rightarrow \left(\frac{N}{N_0}\right)={\left(\frac{1}{2}\right)}^n$

$\Rightarrow \left(\frac{1}{4}\right)={\left(\frac{1}{2}\right)}^{n}orn=2$

T = $n\times t_{1/2}=\frac{2}{2}=1hr.$