A highly reacting element X is stored under water. It readily reacts with oxygen of air to give a compound Y which dissolves in water. The aqueous solution of Y changes blue litmus solution to red. The element X is

Options

A. sodium
B. Sulphur
C. phosphorus
D. Potassium

Explanation

To solve the question, let's break it down step by step.

### Step 1: Identify the properties of element X
- The question states that element X is highly reactive and is stored under water. This indicates that X is likely a metal that reacts vigorously with air and moisture.

**Hint:** Think about metals that are highly reactive and require storage in water to prevent them from reacting with air.

### Step 2: Determine the reaction of element X with oxygen
- Element X reacts readily with oxygen in the air to form a compound Y. This suggests that Y is likely an oxide of X.

**Hint:** Consider the types of oxides that can form from highly reactive metals.

### Step 3: Analyze the properties of compound Y
- The question states that the aqueous solution of Y changes blue litmus paper to red. This indicates that Y is acidic in nature.

**Hint:** Remember that acidic solutions turn blue litmus paper red. Think about what types of oxides are acidic.

### Step 4: Identify possible candidates for element X
- Since we are looking for a highly reactive element that forms an acidic oxide, we can consider elements like phosphorus (P) and sulfur (S). However, phosphorus is known to react vigorously with oxygen and is stored under water.

**Hint:** Recall the common properties of phosphorus and sulfur, especially how they react with oxygen.

### Step 5: Confirm the identity of element X
- Phosphorus (P) reacts with oxygen to form phosphorus pentoxide (P4O10), which is acidic and dissolves in water to form phosphoric acid (H3PO4). This matches the description of compound Y.

**Hint:** Think about the reaction products of phosphorus with oxygen and their behavior in water.

### Conclusion
- The highly reactive element X is phosphorus (P), which is stored under water and forms an acidic oxide (Y) when it reacts with oxygen.

**Final Answer:** The element X is phosphorus (P).