If the substance containing neutral atoms can be compressed a lot so that the atoms move closer together and the space between them decreases substantially, the substance is most likely a

Answer is: gas.
In gaseous state there are little or no attractive intermolecular forces between atoms and molecules, so atoms have great kinetic energy and move freely. Gas is distinguished from liquids and solids because gas has vast separation of the individual gas particles.

The duration of a photographic flash is related to an rc time constantly

I'll do it rn and then answer