1.

A sample of a radioactive element has a mass of 10 g at an instant t=0. The approximate mass of this element in the sample left after two mean lives is

Answer»

1.35 G
2.50 g
3.70 g
6.30 g

Solution :Here, t=2 `tau=2xx1.44 T_(1//2)=2.88 T_(1//2)`
As `N/N_0=m/m_0=(1/2)^(t//T_(1//2))=(1/2)^(2.88)`
`THEREFORE m=m_0(1/2)^(2.88)=10(1/2)^2.88 ` g
=10 X 0.1358 g = 1.358 g


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