Final answer:
None of the listed options directly increases the oxygen level in a room, but a fan can help distribute the existing air and oxygen more evenly.
Step-by-step explanation:
The machine that changes air in a room into air with more oxygen is none of the listed options directly. An air purifier removes contaminants from the air but does not increase oxygen levels. A dehumidifier removes moisture from the air, and a humidifier adds moisture to the air; neither alter oxygen content significantly. A fan simply circulates the air without changing its composition.
Devices that actually increase the oxygen concentration, such as oxygen concentrators, are not listed among the options provided. For the purposes of the question, it could be argued that increasing air circulation with a fan may help in more evenly distributing oxygen within a room, but it does not change the oxygen concentration of the air itself.