Which item is considered critical for maintaining safety when using chemicals?

Labeling containers properly is essential for maintaining safety when using chemicals because it ensures that all individuals handling the substances are aware of their contents, associated hazards, and necessary precautions. Clear labels provide critical information regarding toxicity, flammability, and reactivity, which can help prevent accidents and chemical spills. Proper labeling facilitates quick identification and enables users to take appropriate safety measures, such as wearing personal protective equipment and following proper handling procedures.

The other options compromise safety. Using expired chemicals can lead to unpredictable reactions or reduced effectiveness. Storing chemicals in unmarked containers increases the risk of misidentification, leading to potential misuse or accidental mixing of incompatible substances. Mixing different chemicals without proper knowledge of their interactions can result in dangerous chemical reactions, which could cause injury or environmental damage.