Which graph in the following diagrams correctly represents the potential energy $U$ of a pair of nucleons as a function of their separation $r$?

The unit of length convenient on the nuclear scale is a fermi: $1 \; f = 10^{-15} \; m$. Nuclear sizes obey roughly the following empirical relation: $r = r_{0} A^{1/3}$,where $r$ is the radius of the nucleus,$A$ is its mass number,and $r_{0}$ is a constant equal to about $1.2 \; f$. Show that the rule implies that nuclear mass density is nearly constant for different nuclei. Estimate the mass density of a sodium nucleus.

The radius of a nucleus is given by $r = r_0 A^{1/3}$,where $r_0 = 1.3 \times 10^{-15} \, m$ and $A$ is the mass number of the nucleus. The lead nucleus has $A = 206$. The electrostatic force between two protons at diametrically opposite points in this nucleus is approximately ................ $N$.

The radius of germanium $(Ge)$ nuclide is measured to be twice the radius of ${ }_4^9 Be$. The number of nucleons in $Ge$ will be

The ratio of the nuclear radii of elements with mass numbers $216$ and $125$ is

What is the particle $x$ in the following nuclear reaction :
${ }_4^9 Be+{ }_2^4 He \rightarrow{ }_6^{12} C+x$