Where are oxygen molecules most dense

oxygen molecules are most dense in the air because theres no other form other than co2 or h2o if you wan tot count in those molecules by far h2o would be most dense air has a low density of 4gs but water is a solid 1

Explanation:

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.