Answers to Hydrogen burning vs Hydrogen fusing explain that in astrophysics "burning" generally refers to nuclear fusion or at least nuclear reactions1, and information at
- Why didn't we see those campfires on the Sun until now?
- What could be the cause of solar "campfires"?
explains that those are astronomical nicknames for very small bright bits of plasma recently discovered on the Sun, not actual fires.
But in the Sun's atmosphere there may (or may not) be opportunities for chemical reactions. Certainly in some cool stars the atmosphere even makes dust.
Question: The sun "burns" hydrogen and even has "campfires" on it, but has anyone calculated a rate of some actual chemical burning on the Sun? Any oxidation reactions at all? If not our Sun, is oxidation simulated for some other stellar atmospheres?
1it's hard for me to think of two protons "fusing into a diproton", later beta-decaying for example; feels more like a nuclear reaction, but maybe that's just me.