Sorry guys, I guess I was not detailed. For the call options of QQQQ, for each of the strike prices between $30 and $60, there exists two types of options. I see now that their spreads are equal for the most part, but what are these two options and why do they exist? This is also the case with the put options.
ie. There's a call option with a strike price of $36 with the symbol QQQLJ.X There's another call option with a strike price of $36 with the symbol UQQLJ.X. Their spreads are equal, their last sold price differs by a bit, their volumes differ but their open interest are relatively close.