Zoeb,
Wireless a/b/g use 2.4GHz
Wireless N can use 2.4GHz or 5.0Ghz. It depends on your adapter and your wireless router.
Some wireless N routers work on 5.0GHz ONLY and some are dual band routers and work with both 2.4GHz and 5.0GHz. IEEE 802.11 - Wikipedia explains it but may seem confusing to some people.
A wireless N router can produce faster connection speeds. The people that use the 5.0 band get the fastest speeds. The Wireless N that use 2.4GHz, use dual streams to get a similar result.
A wired connection will always get the fastest speeds and is the reason if you're a gamer, to have a wired connection.
Rick