Please give an explanation as to why Hamlet treats Ophelia the way he does in the nunnery scene in Hamlet.

There are a number of options you have in explaining
Hamlet's behaviour towards Ophelia in Act III scene 1, the famous nunnery scene, where
Hamlet is rather cruel towards her. One of my favourite adaptions of this play is the
Kenneth Brannagh version, which suggests the reason why Hamlet is so cruel towards
Ophelia is that he becomes aware that their conversation is being watched by Polonius
and Claudius. This of course represents a betrayal of Ophelia towards him, and in this
version Hamlet is grief-stricken by yet another betrayal of somebody whom he loves. Yet
if we think about it, how a director stages this scene is necessarily going to revolve
around a question that the text does not answer for us: is Hamlet aware of Claudius and
Polonius and at what point does he become aware of
them?

The way a director answers this question will of
course have massive ramifications in terms of Hamlet and how his character is played in
this scene. If he remains ignorant of their presence, then this scene strongly suggests
Hamlet's madness and the way that he is losing control of himself. If he is aware of
their presence, this could be a scene where he uses Ophelia, just as Ophelia has used
him, to continue to present his "antic disposition" to the King. Being aware of the
presence of Polonius and Claudius also gives another further option: Hamlet is so cruel
to Ophelia because she has been so cruel to him in betraying him and setting him
up.