The mass number of a nucleus is – (1) always less than its atomic number (2) always more than its atomic number (3) always equal to its atomic number (4) sometimes more - and somtimes equal to its atomic number
(4) sometimes more - and somtimes equal to its atomic number Explanation: Mass number = protons or mass of electron (atomic number) + neutrons. So it is mostly greater than the atomic number. At best, it can be equal to the atomic number.