Correct option- a
Deciding in advance as what is to be done, when it is to be done and who is to do it is planning function of management.
Explanation:
Planning is a psychological process of thinking and deciding in advance what is to be done, how it is to be done, when it is to be done and by whom it is to be done. It is a mental activity in which the manager decides the goals that are to be achieved and the actions through which those goals are to be achieved.