The reaction in which a nucleophile replaces already existing nucleophile in a molecule is called nucleophilic substitution reaction. Haloalkanes are substrate in these reactions. In this type of reaction, a nucleophile reacts with haloalkane (the substrate) having a partial positive charge on the carbon atom bonded to halogen. A substitution reaction takes place and halogen atom, called leaving group departs as halide ion. Since the substitution reaction is initiated by a nucleophile, it is called nucleophilic substitution reaction.

It is one of the most useful classes of organic reactions of alkyl halides in which halogen is bonded to sp3 hybridized carbon.

What is the product formed when ethyl bromide reacts with KNO₂? 

Ethyl nitrite

The correct answer is option 2. Ethyl nitrite.

When ethyl bromide \((C_2H_5Br)\) reacts with potassium nitrite \((KNO_2)\), it undergoes a reaction known as the Finkelstein reaction under specific conditions. In this reaction, ethyl bromide is converted to ethyl nitrite \((C_2H_5ONO)\), not to be confused with ethyl nitrate.

Finkelstein Reaction

Ethyl bromide reacts with potassium nitrite in the presence of a polar solvent like acetone or DMF (Dimethylformamide). The reaction proceeds by nucleophilic substitution where the nitrite ion \((NO_2^-)\) acts as a nucleophile, replacing the bromine atom in ethyl bromide. This results in the formation of ethyl nitrite \((C_2H_5ONO)\).

The product formed when ethyl bromide reacts with \(KNO_2\) is Ethyl nitrite.