Which of the following is included in a hazard statement?

A hazard statement is designed to convey specific information regarding the hazards associated with a chemical or material. The primary function of a hazard statement is to inform users about the potential risks associated with a substance. In this case, the phrase "Keep out of reach of children" directly addresses safety concerns related to an item's use, particularly its potential dangers to vulnerable populations, such as children. This directive is an essential safety precaution and falls squarely within the realm of hazard communication.

The other options, while they may provide relevant information about the product, do not fulfill the role of a hazard statement in the same way. "For professional use only" indicates the intended audience but does not specify any inherent hazards. "May contain hazardous materials" is more of a cautionary phrase that informs about potential content but lacks direct identification of hazards. Similarly, "Not suitable for indoor use" relates to usage instructions rather than explicitly detailing a hazard posed by the product itself. Therefore, "Keep out of reach of children" aligns most closely with the definition and purpose of hazard statements in conveying risks.