1) REBBI YOCHANAN'S QUESTION: DOES "TIKROVES AVODAH ZARAH" LOSE ITS "TUM'AH"?
OPINIONS: Rebbi Yochanan asks whether food which is Tikroves Avodah Zarah loses its states of being Tamei because it is Tikroves Avodah Zarah. The Gemara asks why Rebbi Yochanan does not ask his question about Kelim, vessels. The Gemara explains that Rebbi Yochanan had no question about Kelim, because just as vessels become Tahor when immersed in a Mikvah, they became Tahor upon Bitul. Why, though, does he not ask about the Avodah Zarah itself? The Gemara explains that this also did not bother Rebbi Yochanan, because if the prohibition against benefiting from Avodah Zarah is removed after Bitul, the Tum'ah certainly is nullified as well.
His question is only about Tikroves Avodah Zarah, which remains forbidden from benefit forever, even after Bitul. Does the Tikroves remain Tamei just as it remains forbidden from benefit, or does Bitul work to remove the Tum'ah, since the Tum'ah is only mid'Rabanan, while Bitul does not work to remove the Torah prohibition against benefiting from the object? The Gemara leaves this question unanswered.
(a) RASHI (DH v'Tiba'i Lei Kelim) understands that the Gemara asks why Rebbi Yochanan does not ask his question about vessels that were Tashmishei Avodah Zarah -- vessels used in the service of Avodah Zarah. Rashi continues (DH Keivan) and explains that the Gemara answers that because the "Mikvah" for these vessels is Bitul, their Tum'ah is removed as soon as they are nullified (Bitul works for Tashmishei Avodah Zarah). Rashi then states (DH v'Tiba'i Lei Avodas Kochavim) that when the Gemara asks about Avodah Zarah itself, it refers to food which is Avodah Zarah.
(b) TOSFOS (52b, DH Keivan) learns that when the Gemara earlier asks why Rebbi Yochanan does not ask about vessels, it is asking about vessels which are Tikroves Avodah Zarah, not vessels which are Tashmishei Avodah Zarah. This explanation is also given by the RA'AVAD (as quoted here by the RITVA).
There seem to be a number of proofs to support Tosfos' explanation. Both Tashmishei Avodah Zarah and Avodah Zarah itself can have Bitul done to them. Why, then, would the Gemara ask about both Tashmishei Avodah Zarah and Avodah Zarah itself? Once the Gemara establishes that if Bitul works, the Tum'ah is also removed, it does not need to ask about both Tashmishei Avodah Zarah and regular Avodah Zarah, because the Gemara's answer is applicable to both! Moreover, the question of Rebbi Yochanan is about food which is Tikroves. It makes sense to assume that when the Gemara asks why Rebbi Yochanan does not ask about vessels, it means to ask why he does not ask vessels which are Tikroves.
The RAMBAN learns like Rashi, and has strong reason to do so. The Ramban understands that, unlike Rav (50b), Rebbi Yochanan maintains that something can become Tikroves Avodah Zarah only if the exact same service was done in the Beis ha'Mikdash ("k'Ein Penim Mamash," see Insights to 51a). Therefore, if the Gemara asks why Rebbi Yochanan does not ask about Kelim, the Gemara cannot be referring to Kelim that were Tikroves Avodah Zarah; there were no vessels offered in the service of the Beis ha'Mikdash! The Gemara must be referring to vessels that are Tashmishei Avodah Zarah! Why does the Gemara not give the same answer for both Tashmishei Avodah Zarah and for its question regarding Avodah Zarah? The Ramban answers that the Gemara often gives one answer and then another, even though one answer could have sufficed for both questions.
This also explains why Tosfos does not learn like the Ramban. Tosfos learns that Rebbi Yochanan agrees with Rav (see Insights to 51a), who rules that Tikroves is created by merely doing an action similar to what was done in the Beis ha'Mikdash. He therefore learns that the Gemara's questions about vessels refers to vessels which are Tikroves Avodah Zarah.
Rashi's explanation, however, remains difficult. Rashi in the previous Gemara agrees with Tosfos, that Rav and Rebbi Yochanan do not argue (see Insights to 51a). Why, then, does Rashi choose to explain that the Gemara's question refers to Tashmishei Avodah Zarah? The CHASAM SOFER suggests that Rashi understands that Kelim are generally not made into Tikroves Avodah Zarah, and therefore the Gemara's question must refer to Tashmishei Avodah Zarah.
The Ramban notes that there is an unresolved difficulty in the position of the Ra'avad (quoted by the Ritva). The Ra'avad has a similar opinion to that of the Ramban (see Insights to 51a) and says that Rav and Rebbi Yochanan are arguing. If that is the case, however, then how can he say that the Gemara here is asking why Rebbi Yochanan does not ask about Kelim which are Tikroves Avodah Zarah? There is no such case according to Rebbi Yochanan, since Kelim were never offered as sacrifices in the Beis ha'Mikdash! (Y. MONTROSE)
2) HALACHAH: WHO MAY DO "BITUL"?
QUESTION: The Mishnah says that an idolater can annul his Avodah Zarah and that of his friends. A Jew cannot be Mevatel the Avodah Zarah of a Nochri, and certainly not that of a Jew.
Can all Nochrim do Bitul to Avodah Zarah?
ANSWER: This question has practical relevance, as the Gemara earlier (43a) implies. The Gemara there quotes Rebbi Yehoshua ben Levi who says that he was traveling with Rebbi Elazar ha'Kapar when he found a ring of Avodah Zarah. Rebbi Elazar ha'Kapar saw a Nochri who was a child and did not say anything to him. He then saw a Nochri who was an adult and commanded him to be Mevatel the Avodah Zarah on the ring. When the Nochri did not comply, Rebbi Elazar slapped him, and then the Nochri was Mevatel it. The Gemara infers from this incident that only one who is familiar with the Avodah Zarah can do Bitul, and not a minor.
Can Bitul be done by an adult Nochri who neither worships nor believes in Avodah Zarah?
The HAGAHOS ASHIRI on the Mishnah here says that a Ger Toshav (a Nochri who has accepted not to worship Avodah Zarah) cannot do Bitul. The SHULCHAN ARUCH (YD 146:5) rules that a minor, a Shoteh, and someone who does not believe in Avodah Zarah cannot be Mevatel Avodah Zarah. The REMA adds that Yishmaelim also cannot be Mevatel Avodah Zarah.
Can an apostate Jew, who serves Avodah Zarah, be Mevatel Avodah Zarah? The PISCHEI TESHUVAH (YD 146:1) quotes the TIFERES L'MOSHE who says that he cannot be Mevatel Avodah Zarah.
Accordingly, it is important that a Jew who seeks to benefit from an object which was an Avodah Zarah make sure that the Nochri who is Mevatel it is a genuine idolater whose Bitul is effective. (Y. MONTROSE)