Question

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

Answer 1

Answer:

2

Explanation:

The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Since helium atom has a atomic mass of 4 u and it has two protons. Two protons contribute 2 u to atomic mass. Hence, it must contain 2 neutrons.

Answer 2

Let no. of neutrons be 'n'

As,

atomic mass = no. of protons + no. of neutrons

4 = 2 + n

4 - 2 = n

Therefore, n = 2