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J.J. Thomson’s experiment demonstrated that

1. the e/m ratio of the cathode-ray particles changes when a different gas is placed in the discharge tube
2. cathode rays are streams of negatively charged ions
3. all the mass of an atom is essentially in the nucleus
4. the e/m of electrons is much greater than the e/m of protons

Correct answer: the e/m of electrons is much greater than the e/m of protons

Solution

J.J. Thomson's experiment demonstrated that cathode rays are streams of negatively charged particles (electrons) and measured their charge-to-mass ratio (e/m), which was found to be much greater than that of protons.

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