Which of the following will not be soluble in sodium hydrogen carbonate?

Options

A. 2,4,6-trinitrophenol
B. Benzoic acid
C. o-Nitrophenol
D. Benzenesulphonic acid

Answer

To solve the question of which compound will not be soluble in sodium hydrogen carbonate (NaHCO3), we need to analyze the acidic strengths of the given compounds in relation to carbonic acid (H2CO3), which is formed during the reaction with sodium hydrogen carbonate.

### Step-by-Step Solution:

1. **Understanding Sodium Hydrogen Carbonate**:
Sodium hydrogen carbonate (NaHCO3) reacts with acids to form sodium salts, carbonic acid (H2CO3), which then decomposes into water (H2O) and carbon dioxide (CO2).

2. **Identify the Compounds**:
The question provides four options. We need to evaluate the acidic strength of each compound compared to carbonic acid (H2CO3).

3. **Acidic Strength Comparison**:
- **Sulfonic Acids**: These are very strong acids and have higher acidic strength than carbonic acid. Therefore, they will be soluble in sodium hydrogen carbonate.
- **Carboxylic Acids**: These also generally have higher acidic strength than carbonic acid and will be soluble in sodium hydrogen carbonate.
- **Phenol**: Phenol has a lower acidic strength than carbonic acid and will not be soluble in sodium hydrogen carbonate.
- **Nitrophenols**: The presence of nitro groups increases the acidic strength of phenols. For example, 2,4,6-trinitrophenol has three nitro groups, which significantly increases its acidity, making it more acidic than carbonic acid. However, ortho-nitrophenol has only one nitro group and is less acidic than carbonic acid.

4. **Conclusion**:
Among the options, ortho-nitrophenol (C) has an acidic strength that is less than that of carbonic acid. Therefore, it will not react with sodium hydrogen carbonate and will not be soluble.

### Final Answer:
The compound that will not be soluble in sodium hydrogen carbonate is **C. Ortho-nitrophenol**.

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