Final answer:
The violin was not a popular instrument during the medieval period; instead, early forms of bowed string instruments were used, with the violin gaining popularity in the Renaissance and Baroque periods.
Step-by-step explanation:
The instrument was not popular during the medieval period among the options provided is the violin. While the recorder, portative organ, and harp were indeed used in medieval music, the violin as we know it today did not gain popularity until later. The medieval period did have early forms of bowed string instruments, such as the vielle or the Byzantine Lyra, which can be seen as predecessors to the modern violin. However, these were distinct from the violin, which developed into the form we recognize during the Renaissance period and later became prominent in the Baroque period.