What is a measure of how closely packed particles of matter are in q certain amount of space

In salt water solution,the salt is the blank

Is this correct if not can u correct me

Equal numbers of moles of he(g), ar(g), and ne(g) are placed in a glass vessel at room temperature. if the vessel has a pinhole-sized leak, which of the following will be true regarding the relative values of the partial pressures of the gases remaining in the vessel after some of the gas mixture has effused?