Which activity is the best demonstration of J. J. Thomson’s use of creativity in his work?

The correct answer is making observations in his experiment. In his cathode ray tube experiment J. J. Thomson proved that the cathode rays are indeed negatively charged particles.

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons

the temperature of the gas, in k, not celsius.