One answer wrong about large US city (3,7)
I believe the answer is:
new orleans
'us city' is the definition.
(New Orleans is a city in Louisiana)
'one answer wrong about large' is the wordplay.
'wrong' is an anagram indicator.
'about' is an insertion indicator.
'large' becomes 'L' (eg in clothes sizes).
'one'+'answer'='oneanswer'
'oneanswer' with letters rearranged gives 'neworeans'.
'neworeans' enclosing 'l' is 'NEW ORLEANS'.
(Other definitions for new orleans that I've seen before include "US city" , "City of Louisiana" , "Devastated city" , "port city in the south" .)