The masses of a proton, neutron, and helium nucleus are $1.0073\,u$, $1.0087\,u$, and $4.0015\,u$ respectively. The binding energy of the helium nucleus is $.........\,MeV$.

$m_{p}$ and $m_{n}$ are the masses of a proton and a neutron, respectively. For an element of mass $M$ having $Z$ protons and $N$ neutrons, which of the following is true?

$A$ nuclide $1$ is said to be the mirror isobar of nuclide $2$ if $Z_1 = N_2$ and $Z_2 = N_1$. $(a)$ What nuclide is a mirror isobar of $_{11}^{23}Na$? $(b)$ Which nuclide out of the two mirror isobars has greater binding energy and why?

The binding energy per nucleon of ${ }_5 B ^{10}$ is $8.0 \,MeV$ and that of ${ }_5 B ^{11}$ is $7.5 \,MeV$. The energy required to remove a neutron from ${ }_5 B ^{11}$ is .......... $MeV$.

The mass of an $\alpha$-particle is . . . . . . .

If an electron and a positron annihilate,then the energy released is