If sodium and chloride ions from salt enter a fish with no energy spent, what type of transport is this an example of?

This is an example of passive transport.

Passive transport is the movement of ions or substances across a cell membrane without the expenditure of energy from the cell. The degree of passive transport relies on the level of permeability of the cell membrane. Filtration, osmosis, facilitated diffusion and simple diffusion are the four major types of passive transport.

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate