The variation of number of undecayed nuclei with time is best represented by
(Where $N_0$-initial number of atoms)
Answer & explanation
Correct answer: option 2
The correct answer is option (2) : 
$N=N_0e^{-\gamma t}$
N is the number of undecayed nuclei at any time t
$N_0$ is the number of nuclei at $t=0$