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# Half life of a radioactive substance A is 4 days . The probability that a nucleus will decay in two half-lives is :

$(a)\;\large\frac{1}{2}\qquad(b)\;\large\frac{1}{4}\qquad(c)\;\large\frac{3}{2}\qquad(d)\;\large\frac{3}{4}$

Answer : (d) $\;\large\frac{3}{4}$
Explanation :
After two half lives $\;\large\frac{1}{4}^{th}\;$ fraction of nuclei will remain undecayed . or $\;\large\frac{3}{4}^{th}\;$ fraction will decay hence the probability that a nucleus decays in two half lives is $\large\frac{3}{4}$