I know you did not put this as one of the answers, but I see the photo you took, and I think the answer is actually 10 the square root of 100 is 10, and a rational number is a number that can be written as a fraction. The other numbers that are there, are all decimals, and can't be written as a fraction. So I don't know if the square root of 100 is a choice, but I think that is actually the answer. Hope this helps. c;