Is Zakat obligatory on the deceased mother's gold teeth that she used to wear, knowing that the gold is 21-karat? And is what is called "Al-Khatma" — which is an gathering of sheikhs and students who recite parts of the Quran for the soul of the deceased, followed by a dinner banquet — permissible or forbidden?

There is no Zakat on gold teeth if they are permanently fixed in the organ, because they are considered as consumed. However, if they can be removed, there is a difference of opinion regarding their Zakat, similar to permissible jewelry. The preponderant view is that permissible jewelry intended for personal use is not subject to Zakat.

However, if these teeth are removed and inherited by heirs, and are not for permissible use, then Zakat is obligatory on them if they reach the nisab — which is 85 grams of 24-carat gold — and a hawl (one lunar year) has passed since the date of the deceased's passing. As for performing a khatmah (recitation of the entire Quran) for the deceased, it is an innovation (bid'ah).