(1) Formic Acid vs Acetic Acid 

Both formic acid and acetic acid are organic molecules that can be categorized as carboxylic acids due to the presence of a carboxyl group. Therefore, both compounds are acidic compounds. However, in aqueous solutions, these are weak acids that are partially dissociated into their conjugated base form by releasing a proton. The main difference between formic acid and acetic acid is that formic acid is composed of a carboxyl group attached to a hydrogen atom whereas acetic acid is composed of a methyl group attached to a carboxyl group.

(2) Phenol vs Benzoic Acid 

Phenol and benzoic acid are organic compounds. Both are aromatic compounds. An aromatic compound is a substance that is composed of a planar ring system with delocalized pi electron clouds. Phenol is the simplest aromatic alcohol. It is considered as a toxic compound. Benzoic acid is the simplest aromatic carboxylic acid. It is not considered as a toxic compound. Both these compounds are composed of a substituted benzene ring. The main difference between phenol and benzoic acid is that phenol is an alcohol whereas benzoic acid is a carboxylic acid.