Mark the correct statement

From the statements given below:$(A)$ The angular momentum of an electron in $n^{\text {th }}$ orbit is an integral multiple of $h$.$(B)$ Nuclear forces do not obey inverse square law.$(C)$ Nuclear forces are spin dependent.$(D)$ Nuclear forces are central and charge independent.$(E)$ Stability of nucleus is inversely proportional to the value of packing fraction.

Choose the correct answer from the options given below :

Choose the correct statement

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?

Write the unit of mass in nuclear physics and define it and it is equivalent to how many kilograms? 

The mass number of a nucleus is