When diazonium salt solution is treated with water at a temperature of 283 K, it forms phenol. Diazonium salts are compounds that contain the diazonium group (-N≡N+) as a cation. These salts are highly reactive and can undergo various reactions.

Explanation:
1. Formation of diazonium salt:
Diazonium salts are usually prepared by the reaction of an aromatic amine with nitrous acid (HNO2). This reaction is called diazotization. In this process, nitrous acid is generated in situ by the reaction of sodium nitrite (NaNO2) with hydrochloric acid (HCl). The amine reacts with nitrous acid to form the diazonium salt.

2. Reaction with water:
When the diazonium salt is treated with water, it undergoes hydrolysis to form phenol. This hydrolysis reaction is known as the Sandmeyer reaction. The reaction proceeds as follows:

- The diazonium salt reacts with water to form a phenol and nitrogen gas. The nitrogen gas evolves as a byproduct of the reaction.

3. Mechanism of the Sandmeyer reaction:
The reaction proceeds through the formation of a diazonium hydroxide intermediate, which then decomposes to yield the phenol and nitrogen gas. The hydrolysis of the diazonium salt involves the following steps:

- The diazonium salt reacts with water to form a diazonium hydroxide intermediate. This intermediate is unstable and decomposes readily.
- The diazonium hydroxide intermediate undergoes a rearrangement to form a phenol and nitrogen gas. The reaction is usually carried out under acidic conditions to promote the rearrangement.

4. Importance of temperature:
The reaction is typically carried out at a lower temperature, such as 283 K, to prevent the formation of side products. At higher temperatures, there is a higher chance of decomposition of the diazonium salt without forming the desired product.

In conclusion, when diazonium salt solution is treated with water at a temperature of 283 K, it undergoes hydrolysis to form phenol. This reaction is known as the Sandmeyer reaction and involves the formation and subsequent decomposition of a diazonium hydroxide intermediate.