Consider the following statements and select correct code 

S₁ : Decomposition of PCl₅ is intra molecular redox reaction

S₂ : SO₂ acts as both oxidizing and reducing agent

S₃ : NH₃ + HCl $\to$NH₄Cl is a redox reaction 

Reaction in  which single element of same compound under goes oxidation and reduction is intramolecular redox reaction

Element whose oxidation state is in between lowest and highest possible oxidation state will acts as both oxidizing and reducing agent.