Which of the following reagents is NOT known to convert aldehydes into carboxylic acids?

The process of oxidizing aldehydes to carboxylic acids is a common transformation in organic chemistry, and several reagents are capable of performing this reaction. Potassium permanganate (KMnO4), chromium trioxide (CrO3), and silver(I) oxide (Ag2O) are all strong oxidizing agents that can effectively convert aldehydes into carboxylic acids.

In contrast, sodium borohydride (NaBH4) is primarily a reducing agent, not an oxidizing agent. Its main role in organic reactions is to reduce carbonyl compounds, including aldehydes and ketones, to their corresponding alcohols. Since NaBH4 does not possess the oxidative capabilities to convert aldehydes into carboxylic acids, it is the correct choice for this question.

This distinction between oxidizing agents and reducing agents is essential in understanding the reactivity of various chemical compounds in organic synthesis.