`A+H_(2)Oto NaOH`
`A underset(400^(@)C)overset(O_(2))rarrBunderset(at25^(@)C)overset(H_(2)O)rarrNaOH+O_(2),`
B is used for oxygenating in submarines A and B are respectively.

Options

A. `Na_(2)O_(2) and Na_(2)O`
B. `Na_(2)O and Na_(2)O_(2)`
C. `Na_(2)O_(2) and O_(2)`
D. `Na_(2)O and O_(2)`

Answer

To solve the problem step by step, we need to identify substances A and B based on the reactions provided.

### Step 1: Identify Substance A
The question states that substance A reacts with water (H₂O) to produce NaOH. We know that sodium oxide (Na₂O) reacts with water to form sodium hydroxide (NaOH).

**Reaction:**
\[ \text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2 \text{NaOH} \]

Thus, we can conclude that:
- **Substance A = Na₂O**

### Step 2: Identify Substance B
Next, we need to determine substance B. The question states that when substance A (Na₂O) reacts with oxygen (O₂) at 400°C, it forms B. The reaction of sodium oxide (Na₂O) with oxygen leads to the formation of sodium peroxide (Na₂O₂).

**Reaction:**
\[ \text{Na}_2\text{O} + \text{O}_2 \rightarrow \text{Na}_2\text{O}_2 \]

Thus, we can conclude that:
- **Substance B = Na₂O₂**

### Step 3: Confirm the Reaction of B
The question also states that when substance B (Na₂O₂) reacts with water at 25°C, it produces NaOH and O₂. This is indeed the case, as sodium peroxide reacts with water to produce sodium hydroxide and oxygen.

**Reaction:**
\[ \text{Na}_2\text{O}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{NaOH} + \text{O}_2 \]

### Conclusion
Based on the above analysis:
- **Substance A = Na₂O**
- **Substance B = Na₂O₂**