In which of the following laboratory situations is it most important that long hair be tied back?

• A. When measuring the mass of a solid using a balance
• B. When preparing solutions in a beaker with cold water
• C. When working with open flames, such as a Bunsen burner
• D. When recording observations in a laboratory notebook

Answer: (C)

Verified step by step guidance

1. Identify the potential hazards associated with each laboratory situation listed.
2. Consider that long hair can easily catch fire if exposed to open flames, such as those from a Bunsen burner.
3. Recognize that measuring mass with a balance, preparing solutions with cold water, or recording observations do not involve fire or heat sources that pose a risk to hair.
4. Understand that tying back long hair is a safety precaution primarily to prevent it from coming into contact with flames or hot equipment.
5. Conclude that the most important situation to tie back long hair is when working with open flames, to avoid fire hazards and ensure personal safety.