Greater the Lewis base strength more stable will be the adduct formed with a Lewis acid. The most stable Lewis acid-base adduct among the following is

Greater the tendency to donate lone pair, more stable will be the Lewis acid-base adduct.Lewis basic strength order is(For the given options),→NH3>PH3>H2O>H2S As Lewis basic strength decreases,lone pair donation tendency decreases,therefore stability of Lewis acid-base adduct decreases.