Which discovery did J. J. Thomson make that improved upon Dalton's atomic theory?

• A. Atoms have a dense, positively charged nucleus.
• B. Atoms are indivisible and cannot be broken down further.
• C. Atoms contain negatively charged particles called electrons.
• D. Atoms combine in fixed ratios to form compounds.

Answer: (C)

Verified step by step guidance

1. Recall Dalton's atomic theory, which proposed that atoms are indivisible and the smallest units of matter.
2. Understand that J. J. Thomson's experiments with cathode rays led to the discovery of particles smaller than atoms.
3. Recognize that Thomson identified these particles as negatively charged, which he called electrons.
4. This discovery showed that atoms are not indivisible but contain internal structure, improving upon Dalton's model.
5. Therefore, Thomson's key contribution was demonstrating that atoms contain negatively charged particles called electrons.