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



We know that nearly all the mass of an atom is because of the nucleus.

The mass of the nucleus is due to the presence of protons and neutrons .


Mass of a proton = Mass of a neutron = 1u



Atomic mass = 4u

Number of protons = 2 → Mass = 2u


Mass of neutrons = atomic mass - mass of protons

              = 4u - 2u

                             = 2u


2 u →  2 neutrons

  1. Class 9
  2. Chapter 4 Class 9 - Structure of Atom (Term 2)

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo