A highly reactive element 'A' is stored under water. It readily reacts with oxygen to give a compound 'B' which dissolves in water. The aqueous solution of 'B' changes blue litmus to red. Identify the element 'A' and compound 'B. Write the reactions involved.

Explanation

To solve the question step by step, we need to identify the highly reactive element 'A' and the compound 'B' it forms when it reacts with oxygen. We also need to write the chemical reactions involved.

### Step 1: Identify Element 'A'
The question states that element 'A' is highly reactive and is stored under water. This suggests that it is a metal that reacts vigorously with air (oxygen) and water. The most common element that fits this description is **Phosphorus (P)**, which is often stored under water to prevent it from reacting with oxygen in the air.

**Hint:** Think about elements that are highly reactive and need to be stored in a way to prevent them from reacting with air.

### Step 2: Identify Compound 'B'
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