# SSC Test Questions The half life period of an isotope is 2 hours. After 6 hours what fraction of the initial quantity of the isotope will be left behind?

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2015-04-29T16:34:32+05:30

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The half life period of an isotope is 2 hours. That means, for every 2 hours, the initial quantity gets halved.
Let 'x' be the initial amount.

After two hours,
x becomes halved. So, the amount of isotope present now is x/2

After next two hours (i.e., after four hours from the beginning),
x/2 becomes halved. So, the amount of isotope present now is (x/2)/2 = x/4

After another two hours (i.e., after six hours from the beginning)
x/4 becomes halved. So, the amount of isotope present now is (x/4)/2 = x/8

Therefore, after six hours, the fraction of initial amount of the isotope left behind will be 1/8 (of x )