Which reagent is commonly used for oxidation in organic synthesis?

Potassium dichromate is a powerful oxidizing agent frequently used in organic synthesis. Its effectiveness stems from its ability to facilitate the oxidation of alcohols to aldehydes and ketones, as well as further oxidizing aldehydes to carboxylic acids. The chromium in potassium dichromate is in the +6 oxidation state, which is reduced during the oxidation reaction, thus enabling the transfer of oxygen to the substrate being oxidized. This makes it a vital tool in various organic reactions where elevation of the oxidation state is required.

The other options do not possess the oxidizing properties characteristic of potassium dichromate. Sodium chloride and sodium bicarbonate are typically neutral reagents, with the former mainly serving as a source of chloride ions and the latter acting more as a buffering agent rather than an oxidizing agent. Hydrochloric acid is a strong acid primarily used for protonation or as a reagent in acid-catalyzed reactions but does not engage in oxidation processes.