Class 12 NEET Physics Atoms and Nuclei Part 1

Number of initial active nuclei=4×1016
Number of decayed nuclei after 10 days (half life)
+=

4×1016

2

=2×1016
Remaining number of nuclei after 10 days
=4×1016−2×1016 =2×1016.
∴ Number of decayed nuclei in next 10 days
=2×10162=1×1016
Similarly, number of decayed nuclei in next 10 days =0.5×1016
∴ Total number of nuclei decayed after 30 days
=2×1016+1×1016 +0.5×1016=3.5×1016.