Explanation:
The presence of carbon in an organic compound can be shown by heating the compound with cupric oxide (CuO). This is known as the copper oxide test or the combustion of organic compounds.

Procedure:
1. Take a small amount of the organic compound in a test tube.
2. Add a small amount of cupric oxide (CuO) to the test tube.
3. Mix the compound and cupric oxide thoroughly.
4. Heat the mixture strongly using a Bunsen burner flame.
5. Observe the changes that occur during the heating process.

Observations:
1. Initially, the organic compound and cupric oxide appear as separate solids.
2. As the mixture is heated, the organic compound undergoes combustion and produces carbon dioxide gas (CO2).
3. The carbon dioxide gas can be identified by passing it through lime water (calcium hydroxide solution), which turns milky due to the formation of calcium carbonate (CaCO3) precipitate.
4. The cupric oxide is reduced to metallic copper (Cu) during the combustion process.

Explanation:
Organic compounds are compounds that contain carbon atoms bonded to other elements such as hydrogen, oxygen, nitrogen, and halogens. Carbon is a unique element that forms the backbone of organic molecules due to its ability to form stable covalent bonds with other atoms.

When an organic compound is heated with cupric oxide (CuO), the carbon in the compound undergoes combustion. Combustion is a chemical reaction in which a substance reacts with oxygen to produce heat, light, and new products. In the case of organic compounds, the carbon atoms combine with oxygen from the cupric oxide to form carbon dioxide gas (CO2). This reaction is exothermic, meaning it releases energy in the form of heat and light.

The production of carbon dioxide gas is a characteristic reaction of organic compounds that contain carbon. By observing the formation of carbon dioxide gas and its reaction with lime water to form a white precipitate of calcium carbonate, we can confirm the presence of carbon in the organic compound.

In contrast, the other options mentioned in the question (heating the compound with sodium, heating the compound on a Bunsen flame, and heating the compound with magnesium) are not specific tests for the presence of carbon in organic compounds. These reactions may have other purposes or may not produce a specific reaction that confirms the presence of carbon. Therefore, option B (heating the compound with cupric oxide) is the correct answer.