OPEC Countries - Sudden Death

Sudan is a member of OPEC+, which is a larger group formed in 2016, comprising OPEC nations plus 11 (originally 10) other countries that joined in an agreement to coordinate oil production rates to "balance" (i.e.: control) oil prices.

So it's similar in principle to OPEC, but isn't exactly the same (and participants are bound by far fewer agreements and resolutions).

Anyway, Sudan is a member of OPEC+ but is not and never has been a member of OPEC. They applied for membership a number of years ago but never received it, and I believe they have since withdrawn that application (following a civil war and regime change) but could be wrong on this point.

TL;DR if a quiz requires (or required) Sudan as an OPEC (vs. OPEC+) membership, then the author was mistaken and that quiz is/was incorrect.

I mean, yes, but the quiz asks about countries that have ever been an OPEC member (emphasis theirs, in the quiz description), not necessarily just current members. So the UAE as an answer is correct.

If you want the quiz with only current members, try the one I linked above