# NEET Physics Nuclei Questions Solved

In a sample of radioactive material, what fraction of the initial number of active nuclei will remain undisintegrated after half of a half-life of the sample
(a) $\frac{1}{4}$        (b) $\frac{1}{2\sqrt{2}}$
(c) $\frac{1}{\sqrt{2}}$     (d) $2\sqrt{2}$

(c) $\therefore \frac{\mathrm{N}}{{\mathrm{N}}_{0}}={\left(\frac{1}{2}\right)}^{\mathrm{t}/{\mathrm{T}}_{1/2}}{\left(\frac{1}{2}\right)}^{1/2}=\frac{1}{\sqrt{2}}$

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