Protons are not the only subatomic particle that has a charge, electrons do to and they are negatively charged. Neutrons are situated in the nucleus of the atom, which means that they do not orbit it. Subatomic particles have different masses.
You are then left with Electrons are the subatomic particles with the smallest mass as your answer.
The highest density among the inert gases is of Neon (Ne). This a factual data. Thus the highest density among given options is of Ne, as all the options are of inert gases.
For example, silver ion can be precipitated with hydrochloric acid to yield solid silver chloride. Because many cations will not react with hydrochloric acid in this way, this simple reaction can be used to separate ions that form insoluble chlorides from those that do not.
