Final answer:
The Prothesis is the name of the chapel in an eastern church where the eucharistic elements are prepared, typically located near the Bema or sanctuary.
Step-by-step explanation:
The name of the chapel in an eastern church where the eucharistic elements are prepared is called the Prothesis. In Byzantine and Orthodox church architecture, this space functions specifically for the liturgical preparation of the bread and wine that will be used during the celebration of the Eucharist. The Prothesis is typically located to the side of the Bema (sanctuary) and may be a separate chamber or a designated area within the sanctuary itself.
Eastern churches often have a layout that includes the narthex at the western end, the naos or nave as the main worship area, and the Bema where the altar is located. The Prothesis, along with the Diakonikon (sacristy), typically flank the Bema. Separation between the naos and Bema is often achieved through a barrier called a templon, which evolved into the iconostasis found in later orthodox churches.