Q.Write the general notation of the nucleus of an element X. What does each term denote?

The nucleus at the centre of every atom is built from two types of particles, collectively called nucleons: protons, carrying positive charge $q=+e$, and neutrons, which are electrically neutral. The number of protons is the atomic number $Z$; the number of neutrons is the neutron number $N$; and the total number of nucleons (protons plus neutrons together) is the mass number $A$, related by

A proton's mass, $1.6726\times10^{-27}$ kg, is roughly 1836 times an electron's mass, while a neutron is very slightly heavier still, at $1.6749\times10^{-27}$ kg.

Any specific nucleus is written using the standard notation $^{A}_{Z}X$, where $X$ is the element's usual chemical symbol, the superscript $A$ is the mass number, and the subscript $Z$ is the atomic number. For example, $^{15}_{7}N$ denotes a nitrogen nucleus with 15 total nucleons, 7 of which are protons ($Z=7$, which is what makes it nitrogen in the first place) and the remaining $N=A-Z=8$ of which are neutrons. Because the chemical symbol $N$ already uniquely fixes $Z=7$, the subscript is often simply dropped in casual usage, and the nucleus written more compactly as just $^{15}N$, spoken as "nitrogen fifteen." …