The atomic masses of two isotopes of an element are $34.98 \ u$ and $36.98 \ u$ and their relative abundances are $75.4 \%$ and $24.6 \%$ respectively. The average atomic mass of the element is: (in $u$)

Given below are two statements $:$ one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ The density of the copper $\left({ }_{29}^{64} Cu \right)$ nucleus is greater than that of the carbon $\left({ }_6^{12} C \right)$ nucleus.
Reason $(R) :$ The nucleus of mass number $A$ has a radius proportional to $A^{1/3}$.
In the light of the above statements,choose the most appropriate answer from the options given below.

Two nucleons are at a separation of $1 \times 10^{-15} \ m$. The net force between them is $F_1$ if both are neutrons,$F_2$ if both are protons,and $F_3$ if one is a proton and the other is a neutron. In such a case:

What kind of force exists between two neutrons?

Obtain approximately the ratio of the nuclear radii of the gold isotope $^{197}_{79}Au$ and the silver isotope $^{107}_{47}Ag$.

Ratio of specific charge of $\alpha$-particle to that of proton is