Answer: B. Compound
Explanation: Compound are the substances which are formed by the combination of two or more elements.
Although the phase of the carbon dioxide is gaseous that is single phase, stll it is not considered as the Homogeneous mixture because in carbon dioxide , both the elements carbon and oxygen reacts with each other chemically to form the gas. This doesnot happen in te mixture.
Thus carbon dioxide is considered as the compound.
