Number 641 is Tornadus, You can only get him on Pokemon White is if you trade with someone who has Pokemon Black. If you take both to The Abundant Shrine (Thundurus and Tornadus) you can unlock Landorus. Be careful though, He's level 70.
Virizion
It is Mismagius.
6
Tornadus.
There are 156 new Pokemon in Black and White, which brings the new total number to 649.
Tornadus is 641st in the Pokedex.
In Pokemon black or white it is number 4 or 3
Look at any pokemon YOU caught. Look at their ID.
4567
Vullaby is the 629th Pokemon.
Lillipup is number 012 in the Unova Pokedex, and 505 in the National.
If you're asking specifically about the Unova Pokedex; there is no number 233. If you are asking about in the National Pokedex, it's Porygon2.