Calculate the number of neutrons present in the nucleus of an element X which is represented as 3115

The atomic number of element X is 15. This means it has 15 protons. The mass number of element X is 31. Mass number = No. of protons + No. of neutrons = 31

∴ The number of neutrons = 31– number of protons = 31–15 = 16

Element X has 16 neutrons.