The oxidation state of P in `PCl_(5) " is " +5`. Since P has fiver 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 " to " +3` or some lower value, therefore, `PCl_(5)` acts as an oxidising agent. For example, it oxidises Ag to `AgCl, Sn " to " SnCl_(4) and H_(2) " to " HCl`
`2overset(0)(A)g + Poverset(+5)(Cl)_(5) rarr2 overset(+1)(A)gCl + Poverset(+3)Cl_(3)`
`overset(0)Sn + 2 overset(+5)PCl_(5) rarr Sn overset(+4)Cl_(4) + 2 overset(+3)PCl_(3)`
`Poverset(+5)Cl_(5) + overset(0)H_(2) rarrPoverset(+3)Cl_(3) + 2 overset(+1)HCl`
