Question

Question 2 unsaved a neutral atom has an atomic number of 20 and a mass number of 42. How many electrons does the atom have?

Answer 1

Atomic number refers to the number of protons an atom has. Since this atom has 20 protons in the nucleus, the charge of the nucleus is +20 (neutrons, also in the nucleus, contribute zero charge). Thus, for the atom to be neutral, its electrons must balance the +20 charge of the nucleus, so it must have 20 electrons.