Reduction of Fehling solution:

Fehling solution is a solution used to test for the presence of reducing sugars. It contains copper sulfate, sodium hydroxide, and potassium sodium tartrate.

When a reducing sugar is present, it will react with the copper ions in the Fehling solution to form a brick-red precipitate of copper(I) oxide.

Reducing agents are compounds that can donate electrons and undergo oxidation themselves. In the case of Fehling solution, reducing sugars are the reducing agents. However, not all compounds can reduce Fehling solution.

Explanation:

Acetic acid cannot reduce Fehling solution because it is not a reducing agent. It does not have the ability to donate electrons and undergo oxidation. The other options, formic acid, formaldehyde, and acetaldehyde, are all reducing agents and can reduce Fehling solution.

Formic acid: It is a strong reducing agent and can reduce Fehling solution.

Formaldehyde: It is also a strong reducing agent and can reduce Fehling solution.

Acetaldehyde: It is a weak reducing agent but can still reduce Fehling solution.

Conclusion:

In conclusion, acetic acid cannot reduce Fehling solution because it is not a reducing agent. The other options, formic acid, formaldehyde, and acetaldehyde, are all reducing agents and can reduce Fehling solution.

Only aldehydes respond to Fehling's solution. So, both formaldehyde and acetaldehyde give positive test to it. Formic acid too gives positive test to it because it has -CHO group but Acetic acid doesn't have any such group so it gives negative testto it.