1. Identify the equilibrium

The given equilibrium is the disproportionation of cuprous ion:

$2Cu^+ \rightleftharpoons Cu(s) + Cu^{2+}$

We are asked: in aqueous medium at $25^\circ C$, this equilibrium shifts towards the left in the presence of which ions.

Shifting left means stabilizing $Cu^+$ relative to $Cu^{2+}$.

2. Use the idea of complex formation

If a ligand forms a stable complex with $Cu^+$, then $Cu^+$ is removed from free solution and becomes more stable. By Le Chatelier's principle, this will oppose disproportionation and shift equilibrium to the left.

If a ligand instead stabilizes $Cu^{2+}$ more strongly, the equilibrium would shift to the right.

So we examine which ligands preferentially stabilize $Cu^+$.

3. Nature of $Cu^+$ and $Cu^{2+}$

• $Cu^+$ is a soft acid.
• $Cu^{2+}$ is relatively harder than $Cu^+$.

According to HSAB principle:

• Soft ligands stabilize $Cu^+$ strongly.
• Hard ligands are less favorable for $Cu^+$.

Now check each ligand.

4. Option A: $NO_3^-$

$NO_3^-$ is a weakly coordinating, relatively hard oxygen-donor ligand. It does not strongly stabilize $Cu^+$.

So it does not shift the equilibrium to the left.

A is incorrect.

5. Option B: $Cl^-$

$Cl^-$ forms complexes such as $[CuCl_2]^-$ with $Cu^+$ and helps stabilize cuprous ion in solution.

Thus $Cu^+$ becomes more stable, so the equilibrium shifts left.

B is correct.

6. Option C: $SCN^-$

$SCN^-$ is a soft/polarizable ligand and stabilizes $Cu^+$ effectively through complex formation.

Hence the equilibrium shifts towards the left.

C is correct.

7. Option D: $CN^-$

$CN^-$ forms very stable cuprous cyanide complexes such as $[Cu(CN)_2]^-$, strongly stabilizing $Cu^+$.

Therefore disproportionation is suppressed and equilibrium shifts left.

D is correct.

8. Final derived answer

The ions that shift

$2Cu^+ \rightleftharpoons Cu + Cu^{2+}$

towards the left are:

$\boxed{Cl^-,\ SCN^-,\ CN^-}$

So the correct options are:

$\boxed{B,\ C,\ D}$

9. Comparison with stored correct answer

Stored correct answer: $B, C, D$

My derived answer: $B, C, D$

They match.