Rational number is the number that can be made into a ratio. The opposite would be irrational number. When you found a square root number, try to make it ratio then solve it. In this case,
0.25= 1/4
√0.25= √(1/4) = 1/2
√0.33=√(1/3)= irrational
The example would be √4 which can become 2 is rational, but √0.33 can't be solved so it is an irrational number