Question

The half life of a radioactive element is 20 min. The time interval between the stages of its 33% and 67% decay is:

• A. $40$ min
• B. $20$ min
• C. $30$ min
• D. $25$ min

Answer 1

The correct option is B $20$ min

Change in 67% to 33% in almost half the concentration change.
$67\%\underset{change}{\overset{Half}{\to }}33.5(\approx 33\%)$
So time interval between the stages of irs 33% and 67% decay is same as $t_{1/2}$ = 20 min.