You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Oxygen

Context:
People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental O
2 supplies.[h] Passengers traveling in (pressurized) commercial airplanes have an emergency supply of O
2 automatically supplied to them in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop. Pulling on the masks "to start the flow of oxygen" as cabin safety instructions dictate, forces iron filings into the sodium chlorate inside the canister. A steady stream of oxygen gas is then produced by the exothermic reaction.

Question:
What gas does the airline exothermic reaction produce?

oxygen gas