How long have you been (in) abroad? Is in unnecessary in this case?
It might seem an easy and beginner question, take that into account, I`ve learnt English since I was 9. But there always questions come up about the grammar
Hi
The word “abroad” is an adverb, so we can never use a preposition with it. It is a rule that preposistions are only used with nouns or noun phrases.
Also, “abroad” is an adjective and we can use it to modify a noun.