Question

Trees help maintain air quality by removing particles from the air. Trees remove ... In addition to removing these particles, trees release oxygen back into the air.

Answer 1

The question is poorly written because plants and trees can also give out Carbon dioxide. BTW the answer is CO2

but why am I saying it is poorly written? Plants also participate in cellular respiration (like all living things). In kreb's cycle (let's see if I remember this correctly haha) the isocitrate and the NAD+ react to give CO2 and NADH. So that CO2 is a byproduct and is forced to be ejected from the plant.

However, plants intake more CO2 to produce glucose in the light independent phase of photosynthesis, wherein it is absorbed from the stomata (C4 and CAM plants are usually more efficient due to low transpiration), which is why it is said to 'remove' carbon dioxide.