Which reagent is commonly used for oxidation reactions?

Potassium permanganate is a strong oxidizing agent commonly used in organic chemistry for oxidation reactions. It contains manganese in a high oxidation state and readily donates oxygen to substrates, facilitating a variety of oxidation processes, such as converting alcohols to ketones or aldehydes, and even to carboxylic acids depending on the reaction conditions and the substrate involved.

The other choices do not serve as effective oxidizing agents in typical organic reactions. Water is a solvent rather than a reagent that promotes oxidation. Bromine water, while useful for bromination reactions, primarily acts as a halogenating agent and is not specifically utilized for oxidation purposes. Sodium chloride, often used as a source of chloride ions, does not participate in oxidation reactions. Therefore, potassium permanganate is the appropriate choice due to its strong oxidizing properties.