6AgNO_4(aq) + PH_3(g) + 3H₂O_(l) → 6Ag_(s) + H₃PO_3(g) + 6HNO_3(aq) In the above reaction, the reducing agent is 

Correct Answer: PH₃(g)

Explanation:

• In redox reactions, the reducing agent is the species that loses electrons (gets oxidized).
• In the given reaction: \[ 6AgNO₃ + PH₃ + 3H₂O \;\;\rightarrow\;\; 6Ag + H₃PO₃ + 6HNO₃ \]
• Silver (Ag⁺) ions from AgNO₃ are reduced to metallic silver (Ag). This means another species must be oxidized.
• Phosphine, PH₃, is oxidized to phosphorous acid, H₃PO₃. - In PH₃, phosphorus has an oxidation state of –3. - In H₃PO₃, phosphorus has an oxidation state of +3. - So, phosphorus is oxidized from –3 to +3.
• Therefore, PH₃ is the reducing agent because it donates electrons that reduce Ag⁺ to Ag.

Hence, the reducing agent is PH₃(g).