You need to trade a Porygon holding an Upgrade.You get an Upgrade from Silph Co building.
Porygon2 is a 2nd gen pokemon and does not appear in Pokemon Red. That aside, both of Porygon's evolutions occur when you trade it while it holds certain item. Up-Grade for Porygon to Porygon2, and Dubious Disc for Porygon2 to Porygon-Z.
if you got the porygon in veilstone(Right to the store second house) if you trade it while it is holdind the up-grade, porygon evoles into porygon2
Give it to a Porygon and trade it. It will evolve into Porygon2.
You can't. Porygon2 is generation 2. Pokemon Yellow is a generation 1 game, so you can't evolve Porygon yet.
Yes you can trade leafgreen version Pokemon to another leafgreen version.
You can only get porygon-z if you trade a porygon2 with an upgrade item only in pearl platinum or diamond version.
You need to find a special item called an Up-Grade first, then trade your Porygon with another player whilst holding the Up-Grade to get a Porygon2.
The dubious disc is used to evolve PORYGON2 into PORYGON-Z a new version exclusive to Diamond/Pearl/Platinum. To evolve PORYGON2 make it hold the disc and trade to a friend then get them to trade PORYGON-Z back.
there are 5 legendary Pokemon in leafgreen version
LeafGreen version does not have Growlithe.
firered and leafgreen version
its only available in Pokemon leafgreen version sorry