Question

The half life of a radioactive substance is 30 days what is the time taken to disintegrate to 3/4^th of its original mass?

• A. 30 days
• B. 15 days
• C. 60 days
• D. 90 days

Answer 1

Answer: (C)

60 days

Answer 2

: Here, $\frac{N_{0} - N}{N_{0}} = \frac{3}{4}$

$\therefore$ no of half lives, n=2

Time taken to disintegrate

$=$Half life × No. of half lives

$= 30 \times 2 = 60days$