A nucleus of uranium decays at rest into nuclei of thorium and helium. Then

In the spectrum of hydrogen, the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is

Consider 3^rd orbit of He⁺ (Helium), using non-relativistic approach, the speed of electron in this orbit will be [given K = 9 $$ \times $$ 10⁹ constant, Z = 2 and h (Planck's Constant) = 6.6 $$ \times $$ 10^$$-$$34 J s]

If radius of the $${}_{13}^{27}$$ Al nucleus is taken to be R_Al, then
the radius of $${}_{53}^{125}$$Te nucleus is nearly