If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm
A
In 8 minutes
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B
In 12 minutes
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C
In 16 minutes
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D
In 20 minutes
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Solution
The correct option is B In 12 minutes
substance reduces to 10 gm (i.e. becomes half in 4 min). So T12=4min. Again M=M0(12)t/T1/2 ⇒10=80(12)t4⇒18=(12)3(12)t4⇒t=12min.