Which of the following particles are constituents of the nucleus

What kind of a force does neutron-neutron ?

The radius of a nucleus of mass number $64$ is $4.8$ fermi. Then the mass number of another nucleus having radius of $4$ fermi is $\frac{1000}{x}$, where $x$ is______.

From the statements given below:$(A)$ The angular momentum of an electron in $n^{\text {th }}$ orbit is an integral multiple of $h$.$(B)$ Nuclear forces do not obey inverse square law.$(C)$ Nuclear forces are spin dependent.$(D)$ Nuclear forces are central and charge independent.$(E)$ Stability of nucleus is inversely proportional to the value of packing fraction.

Choose the correct answer from the options given below :

A heavy nucleus at rest breaks into two fragments which fly off with velocities in the ratio $8 : 1$. The ratio of radii of the fragments is