**Explanation:**

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy. It occurs in the chloroplasts of plant cells and requires several raw materials to take place. The raw materials for photosynthesis include carbon dioxide, water, and sunlight. These raw materials are essential for the production of glucose and the release of oxygen.

**a) Carbon dioxide:**
Carbon dioxide (CO2) is one of the raw materials required for photosynthesis. It is obtained from the atmosphere through small openings called stomata found on the leaves of plants. Carbon dioxide is necessary for the synthesis of glucose during the light-independent reactions of photosynthesis.

**b) Water:**
Water (H2O) is another crucial raw material for photosynthesis. It is absorbed by the roots of plants and transported to the leaves through the xylem vessels. Water provides the necessary hydrogen and electrons for the light-dependent reactions of photosynthesis. It is split during these reactions, releasing oxygen as a byproduct.

**c) Oxygen:**
Oxygen (O2) is not a raw material for photosynthesis. Instead, it is a byproduct released during the light-dependent reactions. These reactions occur in the thylakoid membranes of the chloroplasts and involve the absorption of light energy to produce ATP and NADPH. Oxygen is released into the atmosphere through the stomata during photosynthesis.

**d) None of these:**
The correct answer is option 'C' - oxygen. The other options, carbon dioxide and water, are both raw materials required for photosynthesis. Carbon dioxide is necessary for the light-independent reactions, while water is essential for the light-dependent reactions. Oxygen, on the other hand, is a byproduct of photosynthesis and is released into the atmosphere.

In summary, while carbon dioxide and water are raw materials for photosynthesis, oxygen is not. Oxygen is produced as a byproduct of the process.