Ratio of nuclear radii of ${ }^{135} Cs$ to ${ }^{40} Ca$ is

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 

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

A nucleus disintegrates into two smaller parts, which have their velocities in the ratio $3: 2$. The ratio of their nuclear sizes will be $\left(\frac{x}{3}\right)^{\frac{1}{3}}$. The value of ' $x$ ' is :

If the total binding energies of ${ }_1^2 H ,{ }_2^4 He ,{ }_{26}^{56} Fe$ and ${ }_{92}^{235} U$ nucleiare $2.22,28.3,492$ and $1786 MeV$ respectively, identify the most stable nucleus of the following.

The mass number of nucleus having radius equal to half of the radius of nucleus with mass number $192$ is: