Airport Extreme 802.11ac and the two frequencies

Hi

I am wondering. For the ac protocol, does it work for both 2.4ghz and 5 ghz frequencies or does it only work for 5 ghz frequency.

i used istumbler and I noticed that for my 2.4ghz only a b g and n is broadcasted but for 5 ghz i see only the ac

juat want to confirm is that is the case or do I need to look at other settings

or maybe I just dont understand the whole thing!

ansj64