Final answer:
During photosynthesis, plants convert carbon dioxide and water into glucose and release oxygen as a byproduct. Therefore, the correct answer to the student's question is C. oxygen.
Step-by-step explanation:
During photosynthesis, plants absorb carbon dioxide (CO2) from the air and convert it into carbohydrates, commonly in the form of glucose, and produce oxygen (O2) as a byproduct. The complete equation for photosynthesis can be expressed as:
6CO2(g) + 6H2O(l) + energy from light → C6H12O6(s) + 6O2(g)
This process occurs in the chloroplasts within plant cells, utilizing chlorophyll to capture the energy from light. Importantly, the oxygen produced during photosynthesis is released into the atmosphere, which is crucial for the survival of aerobic organisms including humans. So, to answer the student's question, during photosynthesis plants produce C. oxygen.