Question

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

Answer 1

Given atomic mass $=4\mathrm{u}$

And the number of protons $=2$

Step 1: Formula used:

• The mass of an atom is the sum of the masses of protons and neutrons present in its nucleus.
• So, number of neutrons = Mass number - Number of protons = Atomic mass - Number of protons

Step 2: Putting the values in the formula:

• Number of neutrons = $4-2=2$

Hence, the number of neutrons is $2$.