The hot water bottle adds less than 1/3 of the hot water and immediately puts a stopper on it. Is there any oxygen in the thermos?
Not nearly, but the same. The difference is that the temperature and pressure are different inside and outside.
Because the ratio of expansion and contraction is different, that is, when the air is heated, a variety of molecules in the air are heated away. The proportion of out of the way will lead to changes in the concentration of oxygen.
Yes, of course, but it may be slightly different from the air content because the air contains about 21% oxygen