Q 12-13-021NEETJEE MainMedium
A radioactive sample has $N_0$ nuclei at $t = 0$ and decay constant $\lambda$. The number of nuclei that have decayed after time $t$ is
Answer: (D) $N_0(1 - e^{-\lambda t})$
Undecayed: $N_0e^{-\lambda t}$, so decayed $= N_0 - N_0e^{-\lambda t} = N_0(1 - e^{-\lambda t})$.
Solution by Sreeraj P, M.Sc Physics