The radius of germanium (Ge) nuclide is measured to be twice the radius of $${}_4^9$$Be. The number of nucleons in Ge are

In the reaction $${}_1^2$$H + $${}_1^3$$H $$ \to $$ $${}_2^4$$He + $${}_0^1$$n, if the binding
energies of $${}_1^2$$ H, $${}_1^3$$H and $${}_2^4$$He are respectively a, b and c (in MeV),
then the energy (in MeV) released in this reaction is

The total energy of an electron in the first excited state of hydrogen atom is about $$-$$ 3.4 eV. Its kinetic energy in this state is

Which one of the following pairs of nuclei are isotones ?