Hi Anish,

Yes you can give jee advance 2020 (after appearing for 2020 jee mains and qualifying it), only if you appear for jee examination in 2019 right after qualifying your class 12 examination. This means that in order to be eligible to appear for jee 2020 you must also appear for jee mains 2019.

This is because of the rule that a candidate must have appeared for class12 or equivalent examination either in the same year as he is sitting for jee for the first time or in the just previous year( where he appeared for both jee aas well as class 12 examination)