1.Was tikal and chaos inside the master emerald in sonic & knuckles? 2. Is sonic & knuckles part 2 of Sonic the hedgehog 3? 3.shouldn't Sonic CD come out after sonic the hedgehog 3 and sonic & knuckles? 4. long ago Before sonic was saving south island and stopping robotnik in sonic the hedgehog 1, was that the time shadow got lock in the iron gate? 5. Why was sonic at capitol city instead of station square?
1) For all I know, yes.
2) Sonic 3 was supposed to have 14 Zones(14th being Doomsday), but Sonicteam ran out of time to finish the game so they released it with only 6 Zones. S&K was then released later the same year to complete the game. So, it could be a part 2.
3) Sonic CD took place between Sonic 1 and 2.
4) Yes, Shadow was sealed away into the GUN base 50 years before Sonic was around.
5) It's a new setting to run around in, besides it's not like you could mess around in Adventure Fields.

~ SA Tails