The ratio of the orders of the spacings of nuclear energy levels and atomic energy levels is

The mass of a proton is $1.0073 \; u$ and that of a neutron is $1.0087 \; u$ ($u =$ atomic mass unit). The binding energy of ${ }_2^4 \text{He}$ is (Given: helium nucleus mass $\approx 4.0015 \; u$):

An electron and a positron annihilate each other to produce two $\gamma$-ray photons of equal energy. The minimum energy of each photon is .....

If the binding energy per nucleon in $_3^7Li$ and $_2^4He$ nuclei are $5.60 \, MeV$ and $7.06 \, MeV$ respectively,then in the reaction $p + {}_3^7Li \to 2 {}_2^4He$,the energy of the proton must be ........... $MeV$.

Given below are two statements. One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ The binding energy per nucleon is found to be practically independent of the atomic number $A$,for nuclei with mass numbers between $30$ and $170$.
Reason $(R) :$ Nuclear force is long range.
In the light of the above statements,choose the correct answer from the options given below $:$

$M_n$ and $M_p$ represent the mass of a neutron and a proton, respectively. If an element having atomic mass $M$ has $N$ neutrons and $Z$ protons, then the correct relation is: