What is true photosynthesis?(a)Both carbon dioxide and water are oxidized(b)Both carbon dioxide and water are reduced(c)Carbon dioxide is oxidized and water reduced(d)Carbon dioxide is reduced and water oxidized

The correct answer is: (d) Carbon dioxide is reduced and water oxidized.

Detailed Explanation:
Photosynthesis is a biological process in which green plants, algae, and certain bacteria convert light energy into chemical energy stored in glucose. The overall reaction can be summarized as:

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Reduction of Carbon Dioxide:
Carbon dioxide (CO2) is reduced during the process of photosynthesis. This occurs in the Calvin cycle, where CO2 molecules are converted into glucose (C6H12O6). Reduction means the gain of electrons or hydrogen atoms. CO2 gains electrons provided by NADPH (produced in the light-dependent reactions).

Oxidation of Water:
Water (H2O) is oxidized in the light-dependent reactions of photosynthesis. Oxidation means the loss of electrons. During this step, water molecules are split into oxygen (O2), protons (H+), and electrons through a process called photolysis. The electrons released are used to replace those lost by chlorophyll in Photosystem II.

Thus, in photosynthesis:

Carbon dioxide is reduced to form glucose.
Water is oxidized to release oxygen.
This matches option (d).