To determine which compound is not soluble in sodium bicarbonate, we need to consider the acidity of each compound. Sodium bicarbonate (\text{NaHCO}_3) is a weak base and can only react with sufficiently acidic compounds to form water-soluble salts.
2, 4, 6-Trinitrophenol: Also known as picric acid, it is a strong acid due to the electron-withdrawing effect of the nitro groups. It reacts with sodium bicarbonate to form a soluble salt.
Benzoic acid: It is a weak acid, but it is sufficiently acidic to react with sodium bicarbonate, forming sodium benzoate, which is water-soluble.
O-Nitrophenol: Although it is acidic, it is not as strong as picric acid, and the steric hindrance caused by the ortho-nitro group makes its reactivity with sodium bicarbonate less favorable, thus it is the least likely to form a water-soluble salt.
Benzene sulphonic acid: It is a strong acid due to the presence of the sulfonyl functional group, which can form a soluble salt with sodium bicarbonate.
Thus, among the given options, O-Nitrophenol is the compound that will not be soluble in sodium bicarbonate. This is because its acidity is not strong enough to react completely with sodium bicarbonate to form a salt.
Conclusion: The correct answer is O-Nitrophenol, which is not sufficiently acidic to react with sodium bicarbonate and form a soluble salt.
