Question

cannot be separated by acid or base extraction
choose...
cannot be separated by acid or base extraction
can be separated by a base extraction
can be separated by an acid extraction
choose...

Explanation:

Step1: Recall acid - base extraction principle

Acid - base extraction separates compounds based on their acid - base properties. Acids react with bases and bases react with acids to form salts that are more water - soluble.

Step2: Analyze first pair (toluene and benzaldehyde)

Toluene ($C_6H_5CH_3$) is a non - acidic and non - basic hydrocarbon. Benzaldehyde ($C_6H_5CHO$) is also neither a strong acid nor a strong base. They cannot be separated by acid or base extraction as they do not react with common acids or bases to form water - soluble salts. So the answer for the first pair is "Cannot be separated by acid or base extraction".

Step3: Analyze second pair (toluene and phenol)

Phenol ($C_6H_5OH$) is a weak acid. It can react with a strong base (e.g., NaOH) to form a water - soluble phenoxide ion ($C_6H_5O^-$). Toluene does not react with bases. So they can be separated by a base extraction. The answer for the second pair is "Can be separated by a base extraction".

Step4: Analyze third pair (phenol and benzoic acid)

Both phenol ($C_6H_5OH$) and benzoic acid ($C_6H_5COOH$) are acidic. Benzoic acid is a stronger acid than phenol. But they can be separated by using a weak base like sodium bicarbonate. Benzoic acid reacts with sodium bicarbonate to form a salt while phenol does not. So they can be separated by an acid - base extraction method (using a weak base as an extractant), and the answer is "Can be separated by a base extraction".

Answer:

First pair: Cannot be separated by acid or base extraction
Second pair: Can be separated by a base extraction
Third pair: Can be separated by a base extraction