Atomic number of a nucleus is $Z$ and atomic mass is $M.$ The number of neutron is

Two nucleons are at a separation of $1 \times {10^{ - 15}}m$. The net force between them is ${F_1}$, if both are neutrons, ${F_2}$ if both are protons and ${F_3}$ if one is a proton and other is a neutron. In such a case

An alpha nucleus of energy $\frac{1}{2}m{v^2}$ bombards a heavy nuclear target of charge $Ze$. Then the distance of closest approach for the alpha nucleus will be proportional to

Consider the following statements :

$A.$ Atoms of each element emit characterstics spectrum.

$B.$ According to Bohr's Postulate, an electron in a hydrogen atom, revolves in a certain stationary orbit.

$C.$ The density of nuclear matter depends on the size of the nucleus.

$D.$ A free neutron is stable but a free proton decay is possible.

$E.$ Radioactivity is an indication of the instability of nuclei.

Choose the correct answer from the options given below 

Highly energetic electrons are bombarded on a target of an element containing $30$ neutrons. The ratio of radii of nucleus to that of Helium nucleus is ${14^{1/3}}$. The atomic number of nucleus will be

Two protons exerts a nuclear force on each other, the distance between them is