Consider the following reactions :
I. Ethanol is oxidised by acidified `K_2 Cr_2 O_7`
II. Methane undergoes complete combustion.
III. Ethanoic acid reacts with anhyd.`Na_2 CO_3`.
IV. Ethanol reacts with sodium metal.
Reaction(s) in which water is one of the products is/are

Options

A. I and II only
B. I, II and III only
C. III and IV only
D. II only.

Answer

To determine which reactions produce water as one of the products, we will analyze each reaction step by step.

### Step 1: Analyze Reaction I
**Reaction:** Ethanol is oxidized by acidified K₂Cr₂O₇.

- **Chemical Equation:**
\[ C_2H_5OH + K_2Cr_2O_7 + H_2SO_4 \rightarrow CH_3COOH + Cr_2(SO_4)_3 + K_2SO_4 + H_2O \]
- **Products:** Acetic acid (CH₃COOH), chromium sulfate (Cr₂(SO₄)₃), potassium sulfate (K₂SO₄), and water (H₂O).

**Conclusion:** Water is produced in this reaction.

### Step 2: Analyze Reaction II
**Reaction:** Methane undergoes complete combustion.

- **Chemical Equation:**
\[ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O \]
- **Products:** Carbon dioxide (CO₂) and water (H₂O).

**Conclusion:** Water is produced in this reaction.

### Step 3: Analyze Reaction III
**Reaction:** Ethanoic acid reacts with anhydrous Na₂CO₃.

- **Chemical Equation:**
\[ CH_3COOH + Na_2CO_3 \rightarrow CH_3COONa + CO_2 + H_2O \]
- **Products:** Sodium acetate (CH₃COONa), carbon dioxide (CO₂), and water (H₂O).

**Conclusion:** Water is produced in this reaction.

### Step 4: Analyze Reaction IV
**Reaction:** Ethanol reacts with sodium metal.

- **Chemical Equation:**
\[ 2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \]
- **Products:** Sodium ethoxide (C₂H₅ONa) and hydrogen gas (H₂).

**Conclusion:** Water is NOT produced in this reaction.

### Final Conclusion
The reactions in which water is one of the products are:
- Reaction I (Ethanol oxidized by acidified K₂Cr₂O₇)
- Reaction II (Methane undergoes complete combustion)
- Reaction III (Ethanoic acid reacts with anhydrous Na₂CO₃)

Thus, the correct answer is that water is produced in reactions I, II, and III.