No. See the related link for a list of unobtainable pokemon in Black and White Versions that you must trade for. Also, Keldeo, Meloetta and Genesect are yet to have been released by Nintendo.
Also, some pokemon cannot be "caught" they must be traded (like Thundurus and Zekrom), evolved (like Swadloon to Leavanny and Whirlipede to Venipede), received from the Dream World (like Surskit and Lotad), bred (like Rapidash to Ponyta or Raticate to Rattata) or received from events (like Victini).
You catch them with a ultra ball
Yes you can catch Reshiram in Pokemon black and you can catch zekrom in Pokemon white hope it helped.
You can't catch entei in Pokemon black he is on a different version
No.
You can't catch one.You need to trade it from Pokemon Diamond/Pearl/Platinum version
you cant
You can't catch Dialga in Pokemon Black. You need to trade for it or transfer it from the older Pokemon DS games.
Throw a pokeball at it.
Pokemon Black Version and Pokemon White Version are the same game, except for the pokemon that are available to catch and for certain areas.
In Pokemon Black Version the legendary is Reshiram and Pokemon White its Zerkrom.The only way to get both is to transfer Zerkrom to Pokemon Black Version or Reshiram to Pokemon White Version.
you cant catch it in soulsilver. you have to trade it from diamond pearl or platinum.
Pokemon black has exclusive Pokemon and an exclusive location called black city where you can battle trainers with high leveled Pokemon and you can catch reshiram, while for white version it has more exclusive Pokemon, a exclusive area called white forest where you can catch lower leveled Pokemon of the trainer's Pokemon and you can catch zekrom.