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

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

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the importance of proper chemical handling in the laboratory to ensure safety and prevent contamination or hazardous reactions.
2. Step 2: Recognize that unused chemicals should never be poured down the sink unless explicitly instructed, as this can cause environmental harm or dangerous reactions in plumbing.
3. Step 3: Know that returning unused chemicals to their original containers is unsafe because it can contaminate the stock chemical, potentially causing hazardous reactions or compromising future experiments.
4. Step 4: Be aware that mixing different unused chemicals before disposal is dangerous because unknown reactions may occur, producing toxic gases or explosions.
5. Step 5: Conclude that the correct practice is to follow specific disposal instructions for each chemical and never return unused chemicals to their original containers to avoid contamination.