what is most volatile PH3 or NH3 orH2 or H2O and whas are the reaons

N and P both are Group 15 elements! NH3 have B.P = - 33°c which is greater than of PH3 i.e B. P = -83°C!

Explanation : We know that in Periodic Table from going up to down electronegativity decreases! This is due to increase in the size of atomic radius.

NH3 molecules makes strong intermolecular H bonding b/w themselves. But due to lesser electronegativity of larger PH3 molecules, they cannot form Hydrogen Bonding b/w themselves! Instead of this there is Weak London dispersion force b/w them.

So due to greater attraction in NH3 molecules, they are tightly held. So the Boiling point of NH3 is greater than PH3.

Hence PH3 is more volatile