What is the Atomic Mass of Helium?

Atomic Mass of Helium is  ____________.

A)  6

B)  4

C)  5

D)  3

Answer: The atomic mass of Helium is 4amu. Therefore, the correct option is B.

Explanation:

Atomic Mass of any substance is the sum of the number of protons and the number of neutrons in the nucleus of that atom.

For Helium Atom,

• Number of Protons = 2
• Number of Neutrons = 2

Thus,

Atomic mass of Helium =  2+2 = 4  

In absolute terms, the average atomic mass of Helium is 4.002602 u, which is the proportional mass of its two stable isotopes. The two stable isotopes of the Helium is,

• Helium-3 (₂He³)
• Helium-4 (₂He⁴)