Tornadus, Landorous, Reshiram, Virizion, Terrakion, Cobalion, Kyurem, and Victini.
You have to defeat the elite four then you can catch the legendary
to catch zapdos in pokemon black you have to have every legendary pokemon
you can catch as many legendary Pokemon but only once unless you have it on the computer
You catch them with a ultra ball
Zekrom in Pokemon White and Resharim in Pokemon Black.
In Pokemon black you catch RESHIRAM and TORNADUS In Pokemon white you catch ZEKROM and THUNDERUS Sources : myself
None
In black you can catch Reshiram and tornados. In white you can catch Zekrom and thunderos.
Yes, Reshiram is Black's legendary. You will not be able to catch Zekrom though.
Well it depends what legendary you mean. There are a lot and it would be hard to tell where they all are.
Yes, you catch it in the Giant Chasm.
I put a link to guide on all the legendary pokemon in Pokemon Black in the related links.