Question

The count rate from 100 $cm^{3}$ of a radioactive liquid is c. some of this liquid is now discarded. The count rate of the remaining liquid is found to be c/10 after three half – lives the volume of the remaining liquid, in $cm^{3}$, is.

• A. 20
• B. 40
• C. 60
• D. 80

Answer 1

Answer: (D)

80

Answer 2

: Initial count rate (CR) for 1$cm^{3}$of liquid $= c/100$ after $3$half-lives, CR for $1cm^{3}$ of liquid

$= \frac{1}{8} \times \frac{c}{100}$

Let the volume of the remaining liquid $= Vcm^{3}$

$\therefore$CR of this liquid $V \times \frac{c}{800} = \frac{c}{10}$

Or $V = 80$