Answer;
Always
Explanation;
Firstly, we have to understand what it means for two events to be complementary
When two events are complementary mathematically, it means that for one to occur, the other must not occur.
An example of this is fact that it will rain at a moment, and it will not rain at that same moment in time. Only one of these two can occur at that particular point in time
Now, mutually exclusive events are events that are disjoint in happening. What this mean is that these two events cannot and will not happen at the same time
So, we can see that when two events are complementary, then they are mutually exclusive
So, the correct choice of answer here is that they are always mutually exclusive