First slide
Radio activity
Question

Half life of a radio active element is 1200 yrs. It m0 gm of radio active element existing now, m0/4 gm will remain radio active after

Moderate
Solution

NN0=1(2)t/Tm0/4m0=1(2)t/T1(2)2=1(2)t/T

t/T=2t=2×1200 years 

= 2400 years

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