The half life of a radioactive sample is 20 days and it contains 8 x 1016 active nuclei initially. The number of undecayed nuclei left after 40 days is
1
1.5 × 1016
2
2 × 1016
3
5 × 1016
4
16 × 1016
The half life of a radioactive sample is 20 days and it contains 8 x 1016 active nuclei initially. The number of undecayed nuclei left after 40 days is