You have to determine which of the given square roots can be expressed as a fraction:
1) The square root of one is 1
One can be expressed as a fracion:
So it is a rational number.
2) The square root of 2 is an irrational number and cannot be expressed as a fraction.
Its decimal expantion has no end, i.e. it has infinite decimal values.
3) Square root of three is an irrational number and cannot be expressed as a fraction.
4) The square root of 5 is an irrational number and cannot be expressed as a fraction.
In conclusion the only rational number in the given set is the square root of 1.