Which,among H3PO4 & HCl, is more volatile and why?

Answer 1

HCl is more volatile.
H3PO4 molecules can form hydrogen bonds with each other (which is not the case for HCl) - also they are bigger in size but here the contribution of the hydrogen-bond factor is so big that you don't need to consider the size factor at all .
Thus the intermolecular forces for H3PO4 are greater and it would require much more energy to break these forces so that the molecules can enter the gaseous state.

Answer 2

I think its HCl as it easily dissociates into H+ & Cl-,moreover, Cl- is a stable species in itself.it doesn't need to combine with some other species , as it alredy has a complete octet.thus it can show greater volatility, as compared to PO4 3-,which is formed with difficulty,from H3PO4,which is weaker acid than HCl.Thus it tends to be in company with H+,rather than to go off on its own!Thus,more stable & self-sufficient Cl- has ample opportunity to vaporize.

Answer 3

H3PO4 is more volatile because it has three replaceble hydrogens as compared to HCL which have one