What major event in the play happens just before conclusion of act 3 hamlet?

The major event that happens just before the conclusion of Act 3 of Hamlet is the death of Polonius.

Here's why this is so significant:

* Hamlet's actions: Hamlet, in a fit of anger and believing he is speaking to Claudius, stabs through the curtain, killing Polonius. This action is a turning point in the play, pushing Hamlet further down a dark path.

* Consequences: Polonius's death has immediate and far-reaching consequences. It:

* Sets off a chain of events that leads to Ophelia's madness and death.

* Causes a rift between Hamlet and his mother, Gertrude.

* Creates tension and conflict between Hamlet and the King.

* Exposes Hamlet's madness and his dangerous actions.

Act 3 ends with Hamlet being sent to England, where he faces new dangers and challenges. The death of Polonius sets the stage for the final act, where the consequences of this tragedy will be fully realized.