The grammatically incorrect sentence is:
She is an European.
Correct: She is European.
The adjective "European" does not require an article like "an" before it when used attributively (before a noun). In this case, it modifies the noun "she" and therefore should not have the article.
The other sentences are grammatically correct:
- He is of Asian origin.
- They belonged to Africa.
- They migrated from India to Australia.
Remember, using articles correctly with adjectives can vary depending on their position in the sentence and how they modify the noun. If you're unsure, it's always a good practice to consult a grammar reference guide or check online resources for clarification.
I hope this helps!