IIT-JEE 2011 · Paper 2, Chemistry question 10

Why the left side is favoured. $\ce{Cu+}$ disproportionates in water because aqueous $\ce{Cu^{2+}}$ is strongly hydrated. Ligands that bind Cu(I) much more strongly than Cu(II) reverse this:

• $\ce{Cl-}$ and $\ce{SCN-}$ give insoluble CuCl and CuSCN: $\ce{Cu + Cu^{2+} + 2Cl- -> 2CuCl}$.
• $\ce{CN-}$ gives the very stable $\ce{[Cu(CN)4]^{3-}}$ (and even reduces $\ce{Cu^{2+}}$ to Cu(I)).

$\ce{NO3-}$ binds neither ion.

(B), (C), (D)