The oxidation state of P in `PCl_(5)" is "+5`. Since P has five electrons in its valence shell, therefore, it cannot increase its oxidation state beyond +5 by donating electrons, therefore, `PCl_(5)` cannot act as a reducing agent. However, it can decrease its oxidation number from +5 ot +3 or some lower value, therefore, `PCl_(5)` acts as an oxidisting agent. For example, it oxidises Ag to AgCl, Sn to `SnCl_(4)andH_(2)` to HCl.
`2overset(0)Ag+overset(+5)PCl_(5)to2overset(+1)AgCl+overset(+3)PCl_(3),overset(0)Sn+2overset(+5)PCl_(5)tooverset(+4)SnCl_(4)+2overset(+3)PCl_(3)`
`Poverset(+5)Cl_(5)+H_(2)tooverset(+3)PCl_(3)+2overset(+1)HCl`
In These reacitons, oxidation number of P decreases form +5 in `PCl_(5)` to +3 in `PCl_(3)` and that of Ag and H increases from 0 to +1 and that of Sn from 0 to +4. Thus, `PCl_(5)` acts as an oxidising agent.
