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The half life period of radioactive element x is same ....

The half life period of radioactive element x is same as the mean life time of another radioactive element y. Initially they have the same number of atoms. Then:

(A) x and y have same decay rate initially and later on different decay rate.
(B) x and y decay at the same rate always.
(C) x will decay faster than y.
(D) y will decay faster than x.

Solution

Given, ${({t_{1/2}})_x} = {({t_{mean}})_y}$

$\therefore \frac{{0.693}}{{{\lambda _x}}} = \frac{1}{{{\lambda _y}}}$

$ \Rightarrow {\lambda _x} = 0.693{\lambda _y}$

$ \Rightarrow {\lambda _x} < {\lambda _y}$

If N is same, $A \propto \lambda $

$\therefore A_x < A_y $

Answer: (D)