If the radius of a nucleus with mass number $125$ is $1.5 \text{ fermi}$, then the radius of a nucleus with mass number $64$ is: (in $\text{ fermi}$)

Which of the following is a fundamental force in nature?

Consider the following statements ($X$ and $Y$ stand for two different elements):
$(I)$ ${ }_{32}^{65} X$ and ${ }_{33}^{65} Y$ are isotopes.
$(II)$ ${ }_{42}^{86} X$ and ${ }_{42}^{85} Y$ are isotopes.
$(III)$ ${ }_{85}^{174} X$ and ${ }_{88}^{177} Y$ have the same number of neutrons.
$(IV)$ ${ }_{92}^{235} X$ and ${ }_{94}^{235} Y$ are isobars.
Which of the above statements are correct?

Assume that a neutron breaks into a proton and an electron. The energy released during this process is: ............ $MeV$ (mass of neutron $= 1.6725 \times 10^{-27} \ kg$,mass of proton $= 1.6725 \times 10^{-27} \ kg$,mass of electron $= 9 \times 10^{-31} \ kg$).

The force between a proton and a proton in a nucleus is .......

Which of the following statements is incorrect?