Question

why does bread rise? yeast makes co2 as a waste product using fermentation. yeast makes o2 as a waste product using fermentation.

Explanation:

To determine why bread rises, we analyze the role of yeast in fermentation. Yeast undergoes anaerobic respiration (fermentation) in bread dough, breaking down sugars. The products of this process are ethanol and carbon dioxide ($\ce{CO2}$), not oxygen ($\ce{O2}$). The $\ce{CO2}$ gas produced gets trapped in the dough, causing it to expand or rise. The statement about yeast producing $\ce{O2}$ is incorrect because fermentation (specifically alcoholic fermentation in yeast) does not generate oxygen; it produces $\ce{CO2}$ as a waste product.

Answer:

The correct statement is: Yeast makes $\ce{CO2}$ as a waste product using fermentation.