Question

You roll a six-sided number-cube. Which events are mutually exclusive?

Answer 1

Since you already know the answer. I am going to explain what mutually exclusive (events) means. 

Mutually exclusive means " it cannot or it does not happen on the same time. For instance, doing things at the same time: turning left and turning right, since you cannot turn left and turn to your right at the same time. another one is drawing cards-Kings and Aces. You cannot draw Kings when you draw Aces. 
Mutually not exclusive means, you can do something at the same time. For example, drawing cards--Kings and Hearts. You can draw them at the same time because you have King of Hearts. Another example is, turning left while nodding your head. You can do it at the same time too.
Let us put it this way:
Let X denote the first event and Y for the second event
P for probability.
P (X and Y)=0
This means that the probability of the first and second event is impossible.