An acidic solution.
#"PCl"_ (5(s)) + 4"H"_ 2"O"_ ((l)) -> "H"_ 3"PO"_ (4(aq)) + 5"HCl"_ ((g)) uarr#
Solid phosphorus pentachloride will react with the moisture in the air to produce aqueous phosphoric acid, which, as its name suggests, acts as an acid in aqueous solution, and hydrogen chloride fumes.
The hydrogen chloride fumes are quite acidic themselves. When dissolved in water, hydrogen chloride produces hydrochloric acid, which is a strong acid.
Phosphoric acid, on the other hand, is a weak acid, but an acid nonetheless.
When dissolved in water, phosphoric acid produces an acidic solution which has a