Write the relation of the size of the nucleus to the atomic size.
$1 a.m.u.$ is equivalent to
If the nucleus ${}_{13}^{27}Al$ has a nuclear radius of about $3.6\,\, fm,$ then ${ }_{32}^{125} Te$ would have its radius approximately as .......$fm$
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason $R$. Assertion A : The nuclear density of nuclides ${ }_5^{10} B ,{ }_3^6 Li ,{ }_{26}^{56} Fe ,{ }_{10}^{20} Ne$ and ${ }_{83}^{209} Bi$ can be arranged as $\rho_{ Bi }^{ N }>\rho_{ Fe }^{ N }>\rho_{ Ne }^{ N }>\rho_{ B }^{ N }>\rho_{ Li }^{ N }$.
Reason $R$ : The radius $R$ of nucleus is related to its mass number $A$ as $R=R_0 A^{1 / 3}$, where $R_0$ is a constant.
In the light of the above statement, choose the correct answer from the options given below :
The mass number of a nucleus is
Write the unit of mass and its definition.