Among the properties (a) reducing (b) oxidising (c) complexing, the set of properties shown by $$CN^-$$ ion towards metal species is

Property-by-Property Analysis:

• (a) Reducing Property:

  The cyanide ion can act as a reducing agent in reactions with certain metal ions in higher oxidation states. A classic example is its reaction with copper(II) ions ($$\text{Cu}^{2+}$$), where it reduces copper from the $$+2$$ to the $$+1$$ oxidation state while cyanogen gas ($$(\text{CN})_2$$) is evolved:

  $$2\text{Cu}^{2+} + 4\text{CN}^- \rightarrow 2\text{CuCN} \downarrow + \, (\text{CN})_2 \uparrow$$

  Result: ACTIVE




• (b) Oxidising Property:

  The carbon atom in $$\text{CN}^-$$ is already in a low oxidation state ($$+2$$) and holds a formal negative charge. It does not readily accept electrons from metals to act as an oxidizing agent.

  Result: INACTIVE




• (c) Complexing Property:

  $$\text{CN}^-$$ is classified as a powerful Strong Field Ligand in coordination chemistry. Due to its lone pair availability on carbon and its ability to engage in $$\pi$$-backbonding, it forms exceptionally stable coordination complexes with a wide array of transition metals (e.g., $$[\text{Fe(CN)}_6]^{4-}$$, $$[\text{Ag(CN)}_2]^-$$).

  Result: ACTIVE

The cyanide ion acts both as a complexing agent (c) and a reducing agent (a) toward transition metal species.

Answer: Option C — c, a