Which of the following forms can alum, styptic, and cyanoacrylate be used in a salon or school?

Alum, styptic, and cyanoacrylate are used in salon and school settings for specific purposes, primarily in the context of skin treatments, hair removal, or nail applications. The correct choice being liquid and powder reflects the various forms these substances can effectively take for use.

Alum and styptic typically come in powder form, which can be applied directly to stop bleeding or as astringent, and can also be mixed with liquids to be applied in various treatments. For instance, alum can be dissolved in water to create an astringent solution. Cyanoacrylate is commonly used in the form of liquid adhesives, particularly for nail services, where it bonds artificial nails or nail tips to natural nails.

The other forms listed such as gel, cream, spray, paste, solid, and foam do not encompass the primary forms in which these products are traditionally utilized in cosmetology. While gels and creams may be used for other beauty applications, they do not accurately represent the most common formulations for alum, styptic, and cyanoacrylate products, which emphasize powder and liquid. Thus, focusing on their effective forms in cosmetic treatments substantiates the choice of liquid and powder as the correct answer.