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______.

Atomic weight of boron is $10.81$ and it has two isotopes $_5{B^{10}}$ and $_5{B^{11}}$. Then ratio of  $ _5{B^{10}}{\,:\,_5}{B^{11}} $ in nature would be

A nucleus at rest splits into two nuclear parts having same density and the radii in the ratio $1 : 2$ . Their velocities are in ratio ———

The radius of a nucleus of a mass number $A$ is directly proportional to

$(a)$ Two stable isotopes of lithium $_{3}^{6} L$ and $_{3}^{7} L$ have respective abundances of $7.5 \%$ and $92.5 \% .$ These isotopes have masses $6.01512\; u$ and $7.01600\; u ,$ respectively. Find the atomic mass of lithium.

$(b)$ Boron has two stable isotopes, $_{5}^{10} B$ and $^{11}_{5} B$. Their respective masses are $10.01294 \;u$ and $11.00931\; u$, and the atomic mass of boron is $10.811\; u$. Find the abundances of $_{5}^{10} B$ and $_{5}^{11} B$

An alpha particle is projected towards a stationary ${}_{92}^{235}U$ nucleus with $KE$ kinetic energy find distance of closest approach