The correct answer is:
The skull of Yorik simbolizes Hamlet's obsession with death and decay in act 5.
In the Act 5 Hamlet visits the grave yard and foinds the skull of a man who worked for his father and who he knew as a child, it brings good memories of Hamlet`s childhood when all was well.
Hamlet remembers the dead in the graveyard. "Alas, poor Yorick," exclaimsHamlet, as he recalls that Yorick was "a fellow of infinite jest, of most excellent fancy," one who "hath borne [Hamlet] on his back a thousand times" (5.1.190-191; 191-192; 192-193).