Given below are two statements. One is labelled  Assertion (A) and the other is labelled Reason (R).
In light of the given statements, choose the correct answer from the options given below.

Assertion(A) : Although atom contains equal number of protons and electrons , the atomic number of an element is expressed in terms of protons, but not in terms of number of electrons  present in the nucleus of each of its atoms.

Reason(R) : An atom can easily lose or gain electrons in a chemical reaction to form ions.