Confident is about how you feel about yourself. Arrogant needs somebody to look down on.
Confident is the obvious guess, and it is the wrong half of the idea.
Confidence is entirely self-contained: you can be confident alone in a room. Nothing about it requires anyone else to exist.
Arrogance does. It is a comparison — behaving as if you are better and more important than everyone else. Take the other people away and there is nothing left to be arrogant about.
Behaving as if you are better and more important than everyone else.
Similar: cocky, proud, boastful
confident is not one of the words we teach — it is a word your child already has. That is exactly why it is the one they reach for.
Confident is not among the bank's synonyms for arrogant; proud, boastful and cocky are. Every one of those carries a judgement, and confident does not — which is exactly the judgement a comprehension question tends to be asking about.
Definitions and example sentences on this page are the ones a child sees inside Wordrealm, taken from our list of over 1,100 words. It is free to browse, with nothing to sign up for.
Plain-English guides to each test, from the councils’ own pages: Kent Test · Medway Test · Bucks Secondary Transfer Test