The radioactivity of a given sample of whisky due to tritium (half life `12.3` years) was found to be only `3 %` of that measured in a recently purchased bottle marked `''7` years old''. The sample must have been prepared about.

Options

A. 220 years back
B. 300 years back
C. 400 years back
D. 70 years back

Answer

D

Explanation

(d) After one half life period, the activity of Tritium becomes `50 %`
After `2` half life period `25 %`
After `3` half period `12.5 %`
After `4` half life period `6.25 %`
After `5` half life period `3.12 % ~~ 3 %`
It is `5 xx 12.5 years + 7 years` i.e., approximately `70` years only.