Is Iblis an Angel or a Jinn?
It's well-known that, according to the Quran, Iblis (which is Satan) was a jinn, made out of fire:
He said: What hindered thee that thou didst not fall prostrate when I bade thee? (Iblis) said: I am better than him. Thou createdst me of fire while him Thou didst create of mud.
7:12
And (remember) when We said unto the angels: Fall prostrate before Adam, and they fell prostrate, all save Iblis. He was of the jinn, so he rebelled against his Lord's command.
18:50
He said: I am better than him. Thou createdst me of fire, whilst him Thou didst create of clay.
38:76
However, some people might notice that in the many verses of the Quran, Allah affirms that Iblis is included as one amongst the angels, so it might seem like a contradictory statement:
And when We said unto the angels: Prostrate yourselves before Adam, they fell prostrate, all save Iblis. He demurred through pride, and so became a disbeliever.
2:34
And We created you then fashioned you, then told the angels: Fall ye prostrate before Adam! And they fell prostrate, all save Iblis, who was not of those who make prostration.
7:11
And (remember) when thy Lord said unto the angels: Lo! I am creating a mortal out of potter's clay of black mud altered. So, when I have made him and have breathed into him of My Spirit, do ye fall down, prostrating yourselves unto him. So the angels fell prostrate, all of them together. Save Iblis. He refused to be among the prostrate.
15:28-31
And when We said unto the angels: Fall prostrate before Adam, they fell prostrate (all) save Iblis; he refused.
20:116
When thy Lord said unto the angels: Lo! I am about to create a mortal out of mire, and when I have fashioned him and breathed into him of My Spirit, then fall down before him prostrate, the angels fell down prostrate, every one, saving Iblis; he was scornful and became one of the disbelievers.
38:71-74
In Arabic grammar, there is a well established grammatical category on exceptions; a principle known as Taghlīb (تغليب), according to which, the majority is addressed, even if minorities are included. Using the rule, you can make any sentence you feel like, as long as they are grammatically correct in other aspects. As an example; addressing a class containing 10 students of whom 9 are boys and one is a girl, if I say in Arabic that the boys should stand up, it includes the girl as well and I need not to mention her seperately. For another example; I can say in Arabic: "All the people left except a dog." In English, it would be more suitable to translate this as a new sentence: "All the people left. Only a dog remained."
Similarly in the Quran; when Allah addressed the angels, Iblis was present among them, but it is not required that he be mentioned separately in Arabic. Therefore, according to that sentence, Iblis may be an angel or may not be an angel, but we come to know from 7:12, 18:50 and 38:76 that Iblis was a jinn, made out of fire.
In addition; jinns, just like human beings, have free will, and they may or may not obey Allah's orders. Angels, in the other hand, have no free will in the sense to do whatever they wish and oppose Allah; they always obey Him:
O ye who believe! Ward off from yourselves and your families a Fire whereof the fuel is men and stones, over which are set angels strong, severe, who resist not Allah in that which He commandeth them, but do that which they are commanded.
6:66
Therefore, the question of an angel disobeying Allah is in of itself irrational, and does not arise. This further supplements the stupidly obvious fact that Iblis was a jinn and not an angel.