Which of the following mixtures cannot be prepared ?

Options

A. `NaHCO_(3) + Na_(2)CO_(3)`
B. `Na_(2)CO_(3) + NaOH`
C. `NaHCO_(3) + NaOH`
D. `H_(2)CO_(3) + NaHCO_(3)`

Answer

To determine which of the following mixtures cannot be prepared, we need to analyze each option provided:

1. **Sodium Bicarbonate (NaHCO3) + Sodium Carbonate (Na2CO3)**
2. **Sodium Carbonate (Na2CO3) + Sodium Hydroxide (NaOH)**
3. **Sodium Bicarbonate (NaHCO3) + Sodium Hydroxide (NaOH)**
4. **Hydrogen Carbonate (HCO3-) + Sodium Bicarbonate (NaHCO3)**

### Step-by-Step Solution:

**Step 1: Analyze the first mixture - Sodium Bicarbonate + Sodium Carbonate**
- Sodium bicarbonate (NaHCO3) and sodium carbonate (Na2CO3) can coexist in a mixture without any reaction. Therefore, this mixture can be prepared.

**Step 2: Analyze the second mixture - Sodium Carbonate + Sodium Hydroxide**
- Sodium carbonate (Na2CO3) and sodium hydroxide (NaOH) can also coexist without any significant reaction. Thus, this mixture can be prepared.

**Step 3: Analyze the third mixture - Sodium Bicarbonate + Sodium Hydroxide**
- When sodium bicarbonate (NaHCO3) is mixed with sodium hydroxide (NaOH), they react with each other. In an aqueous solution, NaHCO3 acts as an acid and NaOH acts as a base, leading to the formation of sodium carbonate (Na2CO3) and water (H2O):
\[ \text{NaHCO}_3 + \text{NaOH} \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} \]
- Therefore, this mixture cannot be prepared as it will react to form sodium carbonate.

**Step 4: Analyze the fourth mixture - Hydrogen Carbonate + Sodium Bicarbonate**
- Hydrogen carbonate (HCO3-) is essentially the same as sodium bicarbonate (NaHCO3) when considering the bicarbonate ion. Therefore, this mixture can also be prepared.

### Conclusion:
The mixture that cannot be prepared is **Sodium Bicarbonate + Sodium Hydroxide**.

---