Step-by-step explanation:
An atom holds three sub-atomic particles and these are protons, neutrons and electrons.
Protons have a positive charge, neutrons have no charge and electrons have a negative charge.
Also, when an atom or element is neutral in nature then it means it contains same number of protons and electrons.
For example, sodium element is a neutral atom as it contains 11 protons and 11 electrons.
Thus, we can conclude that for elements to maintain a neutral charge, protons and electrons are the two particles that must have equal numbers.