## Question

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

### Solution

1.35 gm

*t* = 2 * τ *= 2 × 1.44 T = 2.88 T

= 10 × .1358 = 1.358 gm.

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