**Nucleophilic Substitution**

**Explanation:**

Nucleophilic substitution reactions involve the replacement of a leaving group with a nucleophile. In this reaction, sodium ethoxide (NaOEt) acts as a nucleophile and reacts with ethyl iodide (C2H5I) to form diethyl ether (C2H5OC2H5).

1. **Nucleophile:** Sodium ethoxide is a strong nucleophile due to the presence of the ethoxide ion (C2H5O-). The negative charge on the oxygen atom makes it a strong electron donor, which allows it to attack the carbon atom in the ethyl iodide molecule.

2. **Leaving Group:** Ethyl iodide (C2H5I) serves as the leaving group in this reaction. The iodine atom is a good leaving group because it is relatively large and polarizable, which means it can stabilize the negative charge that forms during the reaction.

3. **Reaction Mechanism:** The reaction proceeds through a nucleophilic substitution reaction, specifically an SN2 (bimolecular nucleophilic substitution) mechanism. In this mechanism, the nucleophile attacks the carbon atom bearing the leaving group from the opposite side, resulting in the inversion of configuration.

4. **Formation of Diethyl Ether:** The reaction between sodium ethoxide and ethyl iodide leads to the formation of diethyl ether (C2H5OC2H5). This is an ether that contains two ethyl groups connected by an oxygen atom. The oxygen atom in the diethyl ether molecule is derived from the ethoxide ion.

5. **Overall Reaction:**

C2H5I + NaOEt → C2H5OC2H5 + NaI

6. **Conditions:** Nucleophilic substitution reactions typically occur under basic or neutral conditions. In this case, the reaction is carried out in the presence of sodium ethoxide, which is a strong base. The basic conditions facilitate the formation of the ethoxide ion, which serves as the nucleophile.

7. **Product:** Diethyl ether is a common solvent and is also used as a starting material in various organic syntheses. It has a low boiling point and is highly flammable.

Therefore, the reaction of sodium ethoxide with ethyl iodide to form diethyl ether is termed nucleophilic substitution.