Historical chapter — outside the current JEE Main unit list. These older questions remain available for reference.
Appeared 84 times across 13 years of JEE Main papers — about 6.5 questions a year. Every one of them is below, with a full worked solution.
We have the frequency data for Hydrogen but haven’t run its papers through the pipeline yet. The 84 questions above are counted from official answer keys; the worked solutions follow once each one clears verification.