Black and White 2 are still 5th Gen.
X and Y are 6th gen.

1st gen: Green, Red (Japanese), Red (International), Blue, Yellow
2nd gen: Gold, Silver, Crystal
3rd gen: Ruby, Sapphire, Emerald, FireRed, LeafGreen
4th gen: Diamond, Pearl, Platinum, HeartGold, SoulSilver
5th gen: Black, White, Black 2, White 2
6th gen: X, Y

FireRed, LeafGreen, HeartGold and SoulSilver aren't really right since they are kinda like remakes of older gens with some newer stuff thrown in.
FireRed and LeafGreen are closer to generation one and HeartGold and SoulSilver are closer to generation two
But maybe you mean according to when they came out, which I guess is different to what region the game is in
Kanto being 1st gen (Red, Green/Blue and Yellow, also Fire red and Leaf green)
Johto being 2nd gen (Gold, Silver and Crystal, also Soul Silver and Heart gold)
Hoenn being 3rd gen (Ruby, Sapphire and Emerald)
Sinnoh being 4th gen (Diamond, Pearl and Platinum)
Unova being 5th gen (Black, White, Black 2 and White 2)
I have no idea what the name of the 6th gen region is, But X and Y Will be based there (Duh)
Just sayin