The answer is yes. When two events are mutually exclusive, this means that the two events cannot happen at the same time. For example, getting heads and getting tails after flipping a coin are mutually exclusive events because you can’t get heads AND tails in one flip.
For this problem, we can figure this out by considering all the multiples of 5 that are less than or equal to 20: 5, 10, 15, and 20. However, NONE OF THESE ARE PERFECT SQUARES. This means that, when rolling a 20-sided number cube once, it’s impossible to get a number that is both a multiple of 5 AND a perfect square. The least common multiple of 5 that is a perfect square is 25, but this can’t be on the cube.
Hope this helps!