The answer is D, reactant.
The difference in the concentration of a substance between two areas is called the concentration gradient. When a region has a higher particle concentration than another, this is known as a concentration gradient. A concentration gradient will cause particles in passive transport to diffuse down it from higher concentration to lower concentration until they are evenly spaced.
The gradual separation of a region of high density from a region of low density in a solution in terms of the concentration of a dissolved material. Understanding how ions and particles flow randomly in a solution or gas depends on the concentration gradient.
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Answer:
The correct answer is actually, B) carbon dioxide, nitrogen, oxygen
