Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

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