During photosynthesis $O_2$ is liberated by the oxidation of
A) $H_20$
B) $CO_2$
C) Phosphoglyceraldehyde
D) None

Hint: Oxidation is the process of addition of oxygen to a molecule. During photosynthesis, plants prepare carbohydrates to liberate oxygen using carbon dioxide and water. This process is dependent on sunlight and takes place in the chloroplast of leaves.

Complete answer:
To solve this question, we must know about the process of photosynthesis.
The process of photosynthesis takes place during the day time in the presence of sunlight which helps in activating the reaction centres and releasing electrons.

During photosynthesis, the oxygen is liberated by the photolysis of water. The water molecules split into hydrogen and hydroxyl ions. This hydroxyl ion reacts to liberate oxygen. This was proved by the radio isotopic study. The O-18 a isotroph of oxygen was radio labelled. It was found that the oxygen is obtained from the water and not by carbon dioxide.

Carbon dioxide- The carbon dioxide forms glucose. The path for carbon was studied by radiolabeled carbon. It was found that the carbon dioxide forms glucose and not water.

Phosphoglyceraldehyde- It is the starting material for the synthesis of glucose.

Hence, the correct answer is option (A)

Note: The carbon dioxide is reduced to carbohydrate. This carbohydrate is oxidised by the process of respiration and liberated energy in the form of ATP. The food is stored in the plants as starch which is a polymer of glucose.