The fundamental particles present in the nucleus of an atom are

Which of the following pairs has the identical $e/m$ value?

Which of the following sub-atomic particles is not considered a fundamental constituent of a standard atom?

The nucleus of an atom can be assumed to be spherical. The radius of the nucleus of mass number $A$ is given by $1.25 \times 10^{-13} \times A^{1/3} \ cm$. The radius of the atom is $1 \ \mathring{A}$. If the mass number is $64$,then the fraction of the atomic volume that is occupied by the nucleus is:

$A$ positron has nearly the same weight as that of:

The space between the proton and the electron in a hydrogen atom is $......$.