The event which cannot happen is called.
A) outcome
B) impossible event
C) frequency
D) None of these.

Hint : You should first carefully analyze all the options given in the question and try to deduce logic from it to what the answer can be. It is a direct question

Complete step-by-step answer:
Now let's analyze each option and see what it means.
Outcome : It is the possible outcome of an event.
Impossible event : The portability of an event that cannot happen is also, such an event is called an impossible event.
 Frequency : It refers to the number of times an even value occurs.
 We can clearly see that the answers will be impossible event.
Hence our answers will be option B.

Note : Keeping knowledge of basic terminology of probability like outcome, frequency helps a let in slowing such questions quickly .Also try eliminating the option to reach an answer.