What type of gas is classified as yellow and primarily used for smoke?

The correct answer is classified as "Smoke." Smoke compounds are often represented in yellow and are primarily utilized in various applications, including crowd control and military operations. These smoke-producing agents can obscure vision and create a screen for movement or tactical advantage during operations.

In contrast, the other compounds mentioned in the options have specific purposes: CN (tear gas) is known for its lacrimatory effects, OC (oleoresin capsicum) is a pepper-based irritant mainly used in personal defense sprays, and DM (dimethyl sulfate) is a chemical warfare agent that can cause severe harm. While each of these agents serves significant roles in law enforcement and military operations, they do not specifically signify the yellow classification associated with smoke. Hence, "Smoke" distinctly represents the agent used primarily for creating visual barriers rather than for causing irritation or incapacitation.