Among the fundamental forces,which one of the following is the strongest force?

The atomic weight of boron is $10.81$ and it has two isotopes $_5B^{10}$ and $_5B^{11}$. The ratio of $_5B^{10} : _5B^{11}$ in nature is:

The radius of ${ }_{29} Cu^{64}$ nucleus in Fermi is (given $R_{0}=1.2 \times 10^{-15} \ m$)

Assertion: Isobars are the elements having same mass number but different atomic number.
Reason: Neutrons and protons are present inside the nucleus.

If the radius of a nucleus with atomic number $Z = 50$ is $9 \times 10^{-15} \ m$,what is the electric potential at its surface?

The radius of a nucleus is given by $r = r_0 A^{1/3}$,where $r_0 = 1.3 \times 10^{-15} \, m$ and $A$ is the mass number of the nucleus. The lead nucleus has $A = 206$. The electrostatic force between two protons at diametrically opposite points in this nucleus is approximately ................ $N$.