Which of the following is invalid type of event processor which can be used as...

Pick First is not valid type. Rest all are valid type of event processor.

Choice : https://docs.mulesoft.com/mule-runtime/4.3/choice-router-concept

Round Robin : https://docs.mulesoft.com/mule-runtime/4.3/round-robin

First Successful : https://docs.mulesoft.com/mule-runtime/4.3/first-successful