The ring.
Marvolo Gaunt's Ring
No she didnt....Dumbledore tells Harry that he is a Horcrux
Well if i remember correctly, dumbledore's ring, of course, was a horcrux. When he realized this, he couldn't take it off and the rings power began to destroy him. He manages to confine the curse to his hand when Snape saves his life with the Sword of Griffindor ( because the sword was infused with basilisk vemon , which is one of the few things that can destroy a horcrux).
R.A.B. Tried to take the horcrux to destroy it, he didn't believe in the way that Voldemort was going about things.
From the Gaunt's Horcrux Ring.
Yes, the horcrux inside of Harry Potter
SpoilersSnape kills Dumbledore with avada kedavra. It is later revealed that this is what Dumbledore wanted as he was already dying after being cursed by a horcrux.
It depends what Horcrux your talking about, they do find them all and destroy them all though.
because it was a horcrux. it would help to destroy voldemort
The sword of Gryfiindor.
Ron
I don't remember any numbering scheme; Dumbledore had some suspicions about what the remaining horcruxes might be, but it isn't clear which one would be "#6". I believe the last horcrux suspect he mentioned was the snake, Nagini. That might have been it.