The binding energies of nuclei $\mathrm{X}$ and $\mathrm{Y}$ are $E_1$ and $E_2$ respectively. Two atoms of $\mathrm{X}$ fuse to give one atom of $\mathrm{Y}$ and an energy $Q$ is released. Then,

Two radioactive materials, $A_1$ and $A_2$, have decay constants of $10{\lambda }_0$ and ${\lambda }_0$, respectively. If initially they have the same number of nuclei, the ratio of number of their undecayed nuclei will be $\left(\frac{1}{e}\right)$ after a time

It is given that the half life for certain radioactive element is $5 \text{min.}$ Four nuclei of that element are observed at a certain instant of time. After five minutes

Assertion (A) : It can be definitely said that two nuclei will be left undecayed

Reasoning (R) : After half life i.e. $5$ minutes, half of total nuclei will disintegrate.

So only two nuclei will be left undecayed. Then