Which of the following elements is most important for respiration? carbon oxygen hydrogen nitrogen

Explanation:

Oxygen of course, because carbon is just the product of respiration, and we don't acutally breathe hydrogen or nitrogen - we might inhale them, of course, but we don't use them. They're just expelled.

Oxygen is used in many processes in our bodies both in big ones such as respiration or molecular ones like many cellular processes.

B. / 2 - Oxygen.

Hope it helped,

BioTeacher101