What is formed when amphoteric oxides react with an alkali solution?

Salt and water

The correct answer is option 4. Salt and water

To understand the reaction between amphoteric oxides and alkali solutions, let's consider an example with aluminum oxide \((Al_2O_3)\), which is an amphoteric oxide.

The balanced chemical equation for the reaction between aluminum oxide and sodium hydroxide (an alkali) is as follows:

\[ Al_2O_3 + 6NaOH \rightarrow 2Na_3[Al(OH)_6] \]

Here's a step-by-step explanation:

1. Dissolution of Aluminum Oxide:

Aluminum oxide is amphoteric, meaning it can react with both acids and bases. In the presence of sodium hydroxide \((NaOH)\), aluminum oxide reacts to form a complex ion known as sodium aluminate.

\[ Al_2O_3 + 6NaOH \rightarrow 2Na_3[Al(OH)_6] \]

2. Formation of Sodium Aluminate (Salt):

The product of the reaction is sodium aluminate (\(Na_3[Al(OH)_6]\)), which is a salt. The sodium aluminate is soluble in water and dissociates into ions.

3. Formation of Water:

As a result of the reaction, water (\(H_2O\)) is formed. The hydroxide ions from the alkali react with the amphoteric oxide to form water molecules.

\[ Al_2O_3 + 6NaOH \rightarrow 2Na_3[Al(OH)_6] + 3H_2O \]

In summary, when an amphoteric oxide reacts with an alkali solution, it undergoes a neutralization reaction. The amphoteric oxide acts as an acid, and the alkali acts as a base. The acidic and basic properties are neutralized, leading to the formation of a salt (sodium aluminate, in this case) and water. The general form of the reaction is:

\[ \text{Amphoteric Oxide} + \text{Alkali} \rightarrow \text{Salt} + \text{Water} \]

This type of reaction is characteristic of substances that exhibit amphoteric behavior, where their reactivity can be influenced by the acidity or basicity of the environment in which they are placed.