Pure hydrogen chloride is a colourless gas with a pungent odour.
This substance is made up of molecules ($HCl$).
The colourless aqueous solution of this gas is called chlorhydric acid
During it's dissolution, the substance has been split to hydrogen and chloride ions.
$HCl(g) \longrightarrow H^+ + Cl^-$
Pure sodium hydroxide is a white solid.
The substance is made up of ions associated to form a cristalline lattice ($Na^+OH^-$).
The colourless aqueous solution of this substance is called caustic soda
During it's dissolution, the sodium and hydroxide ions have been liberated and introduced into water.
$Na^+OH^-(s) \longrightarrow Na^+ + OH^-$
