Question

in plants and algae, ____ is/are a byproduct of photosynthesis.
carbohydrates
c₆h₁₂o₆
co₂
o₂
h⁺

Explanation:

Photosynthesis in plants and algae uses carbon - dioxide and water to produce glucose ($C_6H_{12}O_6$) and oxygen. Oxygen is a by - product released into the atmosphere. Carbohydrates (like $C_6H_{12}O_6$) are main products, $CO_2$ is a reactant, and $H^+$ is involved in the process but not a by - product in the traditional sense.

Answer:

D. $O_2$