Question

At any instant the ratio of the amount of radioactive substances is 2 : 1. If their half lives be respectively 12 and 16 hours, then after two days, what will be the ratio of the substances

• A. 1 : 1
• B. 2 : 1
• C. 1 : 2
• D. 1 : 4

Answer 1

Answer: (A)

1 : 1

Answer 2

By using $N = N_{0}\left( \frac{1}{2} \right)^{n}$

⇒ $\frac{N_{1}}{N_{2}} = \frac{(N_{0})_{1}}{(N_{0})_{2}} \times \frac{(1/2)^{n_{1}}}{(1/2)^{n_{2}}} = \frac{2}{1} \times \frac{\left( \frac{1}{2} \right)^{\frac{2 \times 24}{12}}}{\left( \frac{1}{2} \right)^{\frac{2 \times 24}{16}}} = \frac{1}{1}$