Which of the following numbers is irrational?
a fraction with numerator negative 9 and denominator 5, a fraction with numerator square root of 5, a fraction with numerator 7 and denominator 3, square root of 9
a) a fraction with numerator negative 9 and denominator 5
b) square root of 5
c) a fraction with numerator 7 and denominator 3
d) square root of 9