Here's how to determine the relative formula mass (RFM) of a hydrogen molecule (H₂):

* Identify the elements: A hydrogen molecule consists of two hydrogen atoms.

* Find the atomic masses: The atomic mass of hydrogen (H) is approximately 1.

* Calculate the RFM: Since there are two hydrogen atoms in the molecule, the RFM is 1 * 2 = 2.

Therefore, the relative formula mass of a hydrogen molecule (H₂) is 2.