If the total binding energies of ${ }_1^2 H ,{ }_2^4 He ,{ }_{26}^{56} Fe$ and ${ }_{92}^{235} U$ nucleiare $2.22,28.3,492$ and $1786 MeV$ respectively, identify the most stable nucleus of the following.
${ }_{26}^{56} Fe$
${ }_1^2 H$
${ }_{92}^{235} U$
${ }_2^4 He$
Two protons exerts a nuclear force on each other, the distance between them is
Is nuclear force short range or long range ?
Write the definitions of isotopes, isobar and isotone.
Assertion : The binding energy per nucleon, for nuclei with atomic mass number $A > 100$, decreases with $A$.
Reason : The nuclear forces are weak for heavier nuclei.
The ratio of the density of oxygen nucleus $\left({ }_8^{16} O \right)$ and helium nucleus $\left({ }_2^4 He \right)$ is