Question

what is the mass of an atom that has 4 protons, 5 neutrons and 4 electrons? 5 8 9 13

Answer 1

The element with atomic number 4 is Berilium and its atomic mass is 8(4 protones +4 neutrons) and is placed in the second period and II A group.This element shows Valency 2. In other means the answer you are looking for is 8.