The energy of an electron in the ground state of hydrogen atom is -13.6 eV . The kinetic and potential energy of the electron in the first excited state will be

The potential energy between two nucleon's inside a nucleus is minimum at a distance of about

Assertion (A): An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of $180^{\circ}$.

Reason (R): The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus.

The ratio of the nuclear densities of two nuclei having mass numbers 64 and 125 is