Is one half an irrational number?

no. you can think of an irrational number as any number you don't know the last digit of. 1/2 is = to 0.5. because you know 5 is the last digit, it is rational. pi is irrational, because it does not have a last digit, it goes on forever. 10/3 or 3.33333 repeating is rational because you know 3 will be the last digit even if it is infinite. 6.7878787878 repeating would be irrational because it is not known if the 7 or the 8 is the last digit