\[KCN\] reacts readily to give a cyanide with:
(A) Ethyl alcohol
(B) Ethyl bromide
(C) Bromobenzene
(D) Chlorobenzene

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Hint:The ability of the nucleophiles to signify their lone pairs to a positive centre is what is meant by this term. It refers to the rate at which the nucleophile assaults the substrates (R - LG) and is a kinetic term.

Complete Step by Step Solution:
One nucleophile substitutes another in a class of organic reactions known as nucleophilic substitution reactions. It closely resembles the typical displacement reactions we observe in chemistry, in which a more reactive element displaces a less reactive element from its salt solution. The molecule on which substitution occurs is known as the "substrate," and the group that accepts an electron pair and is moved from the carbon is known as the "leaving group." In its final state, the leaving group is a neutral molecule or anion.
The strength or reactivity of the nucleophile is referred to as its nucleophilicity in nucleophilic substitution processes. Therefore, a greater nucleophile replaces a weaker nucleophile from its component in a nucleophilic substitution reaction.
Ethyl bromide will interact with KCN in a reaction known as nucleophilic substitution of alkyl halides (R-X), resulting in the formation of cyanide.
Cyanide ions are present in solution because KCN is mostly ionic. Despite the fact that both C and N atoms are able to donate electron pairs, the attack mostly involves carbon atoms rather than nitrogen atoms because the C-C bond is more stable than the C-N bond.
\[{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}\text{Br + KCN}\overset{\text{alcohol}}{\mathop{\to }}\,{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}\text{CN+KBr}\]
Hence option b is correct.

Note: The chemical compound with the formula KCN is potassium cyanide. This sugar-like-looking, colourless, crystalline salt has a high water solubility. The main applications for KCN are in organic synthesis, electroplating, and gold mining. Smaller applications include chemical polishing and gilding for jewellery. Extremely dangerous potassium cyanide is. Due to hydrolysis, the damp solid releases minute amounts of hydrogen cyanide, which has a bitter almond odour.