PCl₅ (g) gives PCl₃(g) + Cl₂(g) in this equillibrium if we decrease the pressure the reaction is in backword (right) if not please explain .

When pressure is reduced.The reaction proceeds in the direction having less number of gaseous moles.In this reaction, we have 2 moles (1 mole of PCl3 and 1 mole of Cl2) on right hand side and 1 mole (of PCl5) on left hand side.As LHS has less number of gaseous moles, reaction will proceed to LHS, or backwards when pressure is reduced.