What substance is given off when salt is heated gently?

Water

Explanation:

When a salt solution is heated, the solvent (assumedly water) will evaporate at a greater rate because the water molecules have greater energy.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

if you're asking what comes out, it's steam.