Which of the following gases are diatomic except

A diatomic molecule is a molecule composed of two atoms, whether they are of the same element or not. Therefore, the gases that are diatomic have molecules that consist of two atoms. Nitrogen, hydrogen, fluorine, and oxygen are diatomic gases, which means they exist as molecules composed of two atoms of the same element. On the other hand, helium is a monatomic gas, meaning it exists as individual atoms and not as molecules consisting of multiple atoms. Therefore, helium is the gas among the options given that is not diatomic.