Final answer:
The common oxidizing agent in the options is H₂O₂, also known as hydrogen peroxide.
Step-by-step explanation:
The common oxidizing agent in the given options is H₂O₂. Oxidizing agents are substances that gain electrons in a chemical reaction, causing another substance to lose electrons and become oxidized. H₂O₂, also known as hydrogen peroxide, is a powerful oxidizing agent because it readily donates oxygen atoms in reactions.
HCl is a strong acid but not an oxidizing agent. NaOH is a strong base and does not have oxidizing properties. NaCl is a salt and does not act as an oxidizing agent.