The energy equivalent of $1.0 \text{ kg}$ of substance is . . . . . . .

The binding energies of $_1H^2$,$_2He^4$,$_{26}Fe^{56}$,and $_{92}U^{235}$ are $2.22 \ MeV$,$28.3 \ MeV$,$492 \ MeV$,and $1786 \ MeV$ respectively. Which nucleus is the most stable?

The mass of a $H$-atom is less than the sum of the masses of a proton and an electron. Why is this?

For a nucleus ${ }_Z^A X$ having mass number $A$ and atomic number $Z$:
$A.$ The surface energy per nucleon $(b_s) = a_1 A^{2/3}$
$B.$ The Coulomb contribution to the binding energy $b_c = -a_2 \frac{Z(Z-1)}{A^{4/3}}$
$C.$ The volume energy $b_v = a_3 A$
$D.$ Decrease in the binding energy is proportional to surface area.
$E.$ While estimating the surface energy,it is assumed that each nucleon interacts with $12$ nucleons,($a_1, a_2$ and $a_3$ are constants)
Choose the most appropriate answer from the options given below:

$1 \text{ amu}$ is equal to

$A$ 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?