In combined state, carbon occurs as

Options

A. coal
B. petroleum
C. graphite
D. diamond

Answer

**Step-by-Step Solution:**

1. **Understanding Carbon's States**: Carbon can exist in two states: free state and combined state. The free state means carbon exists alone, while the combined state means carbon is bonded with other elements.

2. **Examples of Free State**: In its free state, carbon can be found in forms such as coal, graphite, and diamond. These forms consist solely of carbon atoms and do not combine with other elements.

3. **Examples of Combined State**: In the combined state, carbon is found in various compounds. A notable example is petroleum, which consists of carbon combined with hydrogen and other elements.

4. **Conclusion**: Therefore, in the combined state, carbon occurs as part of various compounds, such as hydrocarbons in petroleum, carbon dioxide (CO2) in the atmosphere, and many organic compounds.

---