The volume occupied by an atom is greater than the volume of the nucleus by a factor of about

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?

Define mass. Write the unit of mass used in nuclear physics and its value in kilograms.

If the ratio of the mass numbers of two nuclei is $27 : 125$, then the ratio of their surface areas is

The volume of a nucleus is directly proportional to

The nuclei ${ }_{6} C^{13}$ and ${ }_{7} N^{14}$ can be described as