Few teachers have been spared the problem of an obstreperous pupil in the class.

Answer: Option C

Awkward : causing difficulty; hard to do or deal with.
Lazy : unwilling to work or use energy.
Unruly : disorderly and disruptive and not amenable to discipline or control.
Sullen : bad-tempered and sulky.
Obstreperous : noisy and difficult to control.

Synonym of Obstreperous is Unruly