Naquada is used to build a lot of stuff, including the gate - used to power staffs and other weapons and used in most generators which are based on Naquada.
Naquadria is a radioactive, very unstable, but much more power version of Naquada - it was artificially created by modifying natural naquada. When they tried to use it as a power source, it was so unstable they couldn't make reliable hyperspace passages with it.
After taking a look back, having not seen it in a while, I'd have to ask, was there any question about it?