Which of the following statements about handling unused chemicals in the laboratory is correct?

• A. Unused chemicals should never be returned to their original containers to avoid contamination.
• B. Unused chemicals should be poured down the sink unless otherwise instructed.
• C. Unused chemicals can be mixed together before disposal.
• D. It is safe to return all unused chemicals to their original containers.

Answer: (A)

Verified step by step guidance

1. Understand the importance of proper chemical handling in the laboratory to ensure safety and prevent contamination.
2. Recognize that returning unused chemicals to their original containers can introduce contaminants, which may cause dangerous reactions or degrade the chemical's purity.
3. Know that pouring chemicals down the sink is generally prohibited unless specific instructions allow it, as it can harm the environment and plumbing systems.
4. Be aware that mixing different unused chemicals before disposal is unsafe because it can lead to hazardous reactions.
5. Conclude that the safest practice is to never return unused chemicals to their original containers to avoid contamination, making this the correct statement.