When an element ${ }_{90}^{232} \mathrm{Th}$ decays into ${ }_{82}^{208} \mathrm{~Pb}$, the number of $\alpha$ and $\beta^{-}$particles emitted respectively are

During the disintegration of a radioactive nucleus of mass number 208 at rest, two alpha particles each with kinetic energy $E$ are emitted. The total kinetic energy of the emitted alpha particles and the daughter nucleus after the disintegration is

If the total energy of an electron in an orbit is positive, then

If $87.5 \%$ of atoms of a radioactive element decay in 6 days, then the fraction of atoms of the element that decay in 8 days is