The least soluble gas is N2 because it is inert and cannot form any strong bonds with water. The other compounds will react with water and dissolve: CO2 + H2O => H2CO3 SO3 + H2O => H2SO4 NH3 + H2O => NH4+ + OH- HCl + H2O => H3O+ + OH- Solution The least soluble gas is N2 because it is inert and cannot form any strong bonds with water. The other compounds will react with water and dissolve: CO2 + H2O => H2CO3 SO3 + H2O => H2SO4 NH3 + H2O => NH4+ + OH- HCl + H2O => H3O+ + OH-.