Introduction:
Sodium hydrogen carbonate, also known as baking soda, is a weak base that can react with acids to form salts and carbon dioxide gas. When an acid reacts with sodium hydrogen carbonate, the resulting products are a salt, carbon dioxide, and water. However, not all compounds are soluble in sodium hydrogen carbonate. In this response, we will determine which compound among the given options (2,4,6 trinitrophenol, benzoic acid, o-nitrophenol, benzenesulphonic acid) will not be soluble in sodium hydrogen carbonate.

Explanation:
When a compound is soluble in sodium hydrogen carbonate, it means that it can undergo a reaction with the base to form a salt. If a compound is insoluble, it means that it will not react with sodium hydrogen carbonate and will not dissolve in it.

1. 2,4,6 trinitrophenol:
2,4,6 trinitrophenol, also known as picric acid, is a strong acid. It contains three nitro groups (-NO2) attached to a phenol ring. The presence of these nitro groups makes it highly acidic and less likely to be soluble in sodium hydrogen carbonate. Therefore, 2,4,6 trinitrophenol will not be soluble in sodium hydrogen carbonate.

2. Benzoic acid:
Benzoic acid is a weak acid with the chemical formula C6H5COOH. It contains a carboxylic acid group (-COOH) attached to a benzene ring. Benzoic acid is slightly soluble in water but can react with sodium hydrogen carbonate to form sodium benzoate, carbon dioxide, and water. Therefore, benzoic acid will be soluble in sodium hydrogen carbonate.

3. o-nitrophenol:
o-nitrophenol is a phenolic compound with a nitro group (-NO2) attached to the ortho position of the phenol ring. It is a weak acid and can react with sodium hydrogen carbonate to form a salt, carbon dioxide, and water. Therefore, o-nitrophenol will be soluble in sodium hydrogen carbonate.

4. Benzenesulphonic acid:
Benzenesulphonic acid is a strong acid with the chemical formula C6H5SO3H. It contains a sulfonic acid group (-SO3H) attached to a benzene ring. Due to the presence of this strong acid group, benzenesulphonic acid will not be soluble in sodium hydrogen carbonate.

Conclusion:
Among the given options, the compound that will not be soluble in sodium hydrogen carbonate is Benzenesulphonic acid (Option D). This is because benzenesulphonic acid is a strong acid and will not undergo a reaction with sodium hydrogen carbonate to form a salt.

Option 'C' is the correct answer.