Final answer:
The unaccompanied sacred song from the medieval Roman Catholic Church is the Gregorian chant, a monophonic form of music essential for liturgy and later serving as a base for polyphonic developments such as the Ars nova.
Step-by-step explanation:
The type of unaccompanied sacred song that developed in the medieval Roman Catholic Church is known as Gregorian chant. This form of music is monophonic, meaning it consists of a single melodic line without any harmonic support or accompaniment. Gregorian chants were named after Pope Gregory I and were an integral part of the liturgical practices.
During the medieval period, this form of music was essential for religious and spiritual expression in the Church. It evolved over time and became a foundation for later musical developments, such as the Ars nova in the high medieval era, which introduced polyphony where multiple musical lines are heard simultaneously.
The type of unaccompanied sacred song that developed in the medieval Roman Catholic Church is called Gregorian chant. It is a monophonic liturgical genre that was predominant during the earlier medieval period. Gregorian chant is characterized by its melodic simplicity and often sung without instrumental accompaniment.