Chemistry MCQ Practice

Hydrogen has three isotopes with mass numbers 1, 2 and 3.

 

What is the total number of possible relative molecular masses that hydrogen gas can have?

 

A)  3

 

B)  4

 

C)  5

 

D)  6

 

 

Answer: C

 

- Hydrogen gas is a diatomic molecule i.e. H₂

 

- Since there are 3 types of H atoms, the molecule can be made up of the following combination of atoms:

 

  ¹H – ¹H
  ¹H – ²H
  ¹H – ³H
  ²H – ²H
  ²H – ³H
  ³H – ³H

 

- Relative molecular mass (M_r) can be obtained by summing the mass number of the atoms in the molecule.

 

- From the combinations above, there will be 5 different M_r: 2,3,4,5,6