A radioactive sample decays by $$63$$% of its initial value in $$10s$$. It would have decayed by $$50$$% of its initial value in
Correct option is A. $$7s$$
A radioactive sample decays by $$63$$% in $$t=\dfrac{1}{\lambda}$$
Hence $$\lambda=1/10$$
$$N=N_0e^{-\lambda t}$$
$$\dfrac{N_0}2=N_0e^{-0.1t}$$
$$0.1t=ln2$$
$$t=6.93s\approx7s$$