Question
Question: If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in 4 minutes, then in ...
If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in 4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm.
A
In 8 minutes
B
In 12 minutes
C
In 16 minutes
D
In 20 minutes
Answer
In 12 minutes
Explanation
Solution
20 gm substance reduces to 10 gm (i.e. becomes half in 4 min. So T1/2=4min. Again M=M0(21)t/T1/2
⇒ 10=80(21)t/4⇒81=(21)3=(21)t/4⇒ t = 12 min.