Veins take blood back to the heart. which gas would be most abundant in a vein that takes blood from muscle cells in the arm back to the heart?

The answer is carbon dioxide hope this helps!. It could also be oxygen but my reasoning is that its all be depleted once its on its return to the heart.

Oxygen

Explanation:

We gain our energy from oxygen , which is funny because Oxygen can break down the very cells that make up our tissues and organs, our bones and blood. It can damage DNA and critical enzymes. It can injure and stiffen our cell membranes, making the movement of nutrients in and out of cells more challenging while ruining our receptors for various hormones including testosterone, insulin, and thyroid. It kills us the same way a piece of metal gets rusty. scary right?