Question

The half life a radioactive element is $30$ days, in $90$ days the percentage of disintegrated part is :-

• A. $13.5\%$
• B. $46.5\%$
• C. $87.5\%$
• D. $90.15\%$

Answer 1

Answer: (C)

$87.5\%$

Since half life is 30 days. After 90 days, disintegrated mass percentage

$=\left(1-{\left(\frac{1}{2}\right)}^{90/30}\right)\times 100$$=\frac{7}{8}\times 100=87.5\%$