The particles of a gas are actually -
electrons or protons
protons or neutrons
atoms or elements
atoms or molecules

The correct option is d) atoms or molecules

Explanation:

Some gases are made up of atoms whereas other gases are made up of molecules. Pure gases are made out of atoms. For example, neon gas will be made up of atoms. Gases which are not pure will be made up of different atoms. For example, carbon dioxide gas is made up of different molecules. Hence, option D is correct.

Other options, like option A, is false because electrons and protons along with neutrons are part of the atom which will make a gas.