Final answer:
Monophonic music is characterized by a single melodic line without accompaniment, and the correct answer is B. Plainchant. This form was widespread in earlier medieval sacred music, unlike the other options which are associated with polyphonic textures prevalent in Renaissance music.
Step-by-step explanation:
The type of music that is monophonic is B. Plainchant. Monophonic music is characterized by a single melodic line without accompaniment or harmonic support. Plainchant, also known as Gregorian chant, is a perfect example of this type of texture. It was prevalent during the earlier medieval period in sacred music.
Speaking of Renaissance music, the other options given (A. Organum, C. Madrigal, D. Motet) are more closely associated with polyphonic textures. Polyphony is characterized by multiple independent melodic lines occurring simultaneously, which contrasts with the single melodic line of monophony.
For example, during the Renaissance, the Italian secular genre of the madrigal became popular, featuring a form that gave rise to elaborate polyphony. Similarly, motets and organum from the medieval and Renaissance periods are also associated with polyphony, having multiple voices in intricate harmony.