We know for a fact that Basilisk venom is one of the few substances strong enough to destroy a Horcrux. Not only does it destroy the one in Tom Riddles diary, but Ron and Hermione also use one of the fangs to destroy Helga Hufflepuffs cup.
Can Avada Kedavra destroy Horcruxes?
Avada Kedavra kills. Horcruxes are the opposite of a human being, so foremost they cant be killed as thats a rather obvious fact about humans.
Why can Horcruxes only be destroyed by basilisk venom?
After being healed, Harry took the fang and stabbed Riddles diary, destroying that Horcrux beyond magical repair. Because Harry had stabbed the Basilisk with the sword, it was imbued with Basilisk venom and was therefore able to destroy Horcruxes and poison opponents that it cuts through as well.
What else could destroy a Horcrux?
Harry Potter and Hermione Granger both used the fangs of Salazar Slytherins Basilisk to destroy Tom Riddles Diary and Helga Hufflepuffs Cup, respectively. This was only achievable as basilisk venom was an extremely destructive substance capable of destroying Horcruxes.
Why didnt the Basilisk kill the Horcrux in Harry?
So why wasnt the Horcrux residing in Harrys head destroyed when he was bitten by the Basilisk? The answer is simple: He didnt actually die. Fawkes quickly healed the bite wound with his phoenix tears just in time.
Did Harry ever use Avada Kedavra?
In the final battle, Harry used his signature spell with defiance. This time he was more experienced but in some ways he was still guessing, with his assumptions about the Elder Wand. Voldemorts signature spell was Avada Kedavra. Harrys was Expelliarmus.