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?

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8 minutes

12 minutes

16 minutes

20 minutes

answer is B.

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Detailed Solution

20 gm substance reduces to 10gm (i.e., becomes half in 4 min. So T1/2 =4 min. Again M=M012t/T1/2⇒10=8012t/4⇒18=123=12t/4 ⇒t=12 min.

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