Q.:- Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
Answer:-
Mass number of Helium = 4
Number of protons = 2
Number of neutrons(n) = Number of Mass(A) — Number of proton (P)
= 4 – 2 = 2
Thus, No. of neutrons = 2