Question

The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$ th of its original mass to disintegrate will be :

• A. 120 days
• B. 130 days
• C. 180 days
• D. 20 days

Answer 1

Answer: (C)

$7/8$ disintegrates means $1/8$ remains
Or ${\left(\frac{1}{2}\right)}^3$
$\therefore 3$ half lives
$=180$ days