Two nuclei have their mass numbers in the ratio of 1 : 3. The ratio of their nuclear densities would be

Two radioactive materials X₁ and X₂ have decay constants $$5\lambda $$ and $$\lambda $$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X₁ to that X₂ will be 1/e after a time

The ground state energy of hydrogen atom is $$-$$ 13.6 eV. When its electron is in the first excited state, its excitation energy is

If M(A; Z), M_p and M_n denote the masses of the nucleus $${}_Z^AX,$$ proton and neutron respectively in units of u (1 u = 931.5 MeV/c²) and BE represents its bonding energy in MeV, then