Question

The atomic particle whose number in the atoms of an element always remains the same and which forms the real basis for the modern classification of elements is:

(a) electron
(b) proton 
(c) neutron
(d) meson

Answer 1

(b) Proton.
Proton is an atomic particle whose number in the atoms of an element remains the same always, and forms the real basis for the modern classification of elements.