The equilibrium Cu 0 + Cu II ⇌ 2Cu I In aqueous medium at 25oC shifts towards the left in the presence of (1) C l - (2) C N - (3) SC N - (4) N O 3 -

Step-by-step solution

C u 2 + ions will react with C N - and SC N - forming [ Cu ( CN ) 4 ] 3 - and [ Cu ( SCN ) 4 ] 3 - leading the reaction in the backward direction. C u 2 + + 2C N - → Cu C N 2 2Cu ( CN ) 2 → 2CuCN + C N 2 CuCN + 3C N - → [ Cu CN ) 4 3 - C u 2 + + 4SC N - → [ Cu SCN ) 4 3 - C u 2 + also combines with CuC l 2 which reacts with Cu to produce CuCl pushing the reaction in the backward direction. CuC l 2 + Cu → 2CuCl ↓