Among the properties (A) reducing (B) oxidizing (C) complexing, the set of properties shown by CN- ion towards metal species is: (a) \(\mathrm{A}, \mathrm{B}\) (b) B, C (c) \(\mathrm{C}, \mathrm{A}\) (d) \(\mathrm{A}, \mathrm{B}, \mathrm{C}\)

A reducing agent, in chemical terms, is a substance that donates electrons to another compound during a redox (reduction-oxidation) reaction, causing the reduction of the latter substance. This donation leads to the reducing agent itself being oxidized. In the context of the cyanide ion (CN-), it plays the role of a reducer because it has an electron-rich carbon atom which can readily donate its electrons to other species, allowing CN- to reduce metal ions and other positive ions by taking on their positive charge.

Understanding the role of CN- as a reducing agent is crucial in many industrial processes, such as metal purification and electroplating, where CN- ions help to transfer electrons, leading to the gain of electrons (reduction) by metal ions. An illustrative example could be the cyanide process for gold extraction, where CN- reduces gold from its compound, aiding in the extraction of pure gold.

The complexing ability of an ion refers to its capability to form a coordinate covalent bond with metal ions, resulting in the creation of a complex ion or a coordination compound. CN-, because of its lone pair of electrons on the carbon atom, showcases an excellent complexing ability. These lone pairs can be donated to a metal ion forming a stable arrangement known as a coordination complex.

The ability to form such complexes is widespread in applications ranging from industrial catalysis to biological systems. In metallurgy, for example, CN- ions are used to bind to precious metals, forming soluble complexes that are easier to isolate during processing. The stability of these complexes is pivotal, as it influences the separation and purification processes of the metals like gold and silver from their ores.

A coordinate covalent bond is a kind of chemical bond where one atom provides both electrons for the shared pair in a covalent bond. This is different from a regular covalent bond where each atom supplies one electron. CN- ion's ability to form coordinate covalent bonds is due to the lone pair of electrons found on the carbon atom. When CN- approaches a metal ion, the carbon's lone pair is shared with the empty orbital of the metal ion, securing a strong bond characteristic of metal complexes.

This bond is integral to the structure and stability of complexes that CN- forms with metals. The strength and directionality of coordinate covalent bonds are decisive factors in the geometry and reactivity of metal complexes, influencing their behavior in various chemical reactions. Therefore, understanding these bonds helps to predict the structure and properties of complex metal ions that involve CN-.