* Diatomic Gas: A diatomic gas is composed of two atoms of the same element bonded together.

* Atomic Mass: The mass of a diatomic gas is twice the atomic mass of the individual atom.

Calculation:

1. Divide the mass by 2: 160 amu / 2 = 80 amu

2. Identify the element with atomic mass 80 amu: The element with an atomic mass of 80 amu is bromine (Br).

Therefore, the element that forms a diatomic gas with a mass of 160 amu is bromine (Br). The diatomic gas is Br₂ (bromine gas).