4th Gen gen iv to v

can i trade a gen 4 pokemon from pokemon white (gen 5) to platinum?

No you can't. Once you've transferred a Pokemon from Gen IV to V via Poke Transfer, it can't come back to its original game.

no a gen 4 pokemon caught on white transfered to gen 4 game

No. White can only connect to Black, Black 2, White 2 or another copy of White. It can't connect to Gen IV games except by Poke Transfer.

ok but i cant send pokemon out to platinum can i from my white?

No, you can only send Pokemon from your White to Black, Black 2 or White 2. Pokemon that you transfer to a Generation V game cannot be transferred back. Platinum can have pokemon transferred to White, if that's what you're saying; but be aware that once you do transfer them, you will not be able to get them back onto Platinum.

In saying that, I'm going to close this as your question has been answered and as this would usually belong in the Fourth Generation Help Thread sticky at the top of this board. Please use that next time if you have any other queries! :3

Closed.