Which one of the following words is most opposite to the meaning of the word 'undisputed' as used in the passage?

'Undisputed' means not challenged or questioned, universally accepted. Its antonym is something that is challenged or contested. 'Challenging' best conveys this opposite meaning—if something is undisputed, no one challenges it; the opposite is that something is being challenged. 'Doubtful' refers to uncertainty rather than active opposition. Hence (1) Challenging is the best antonym.