Which number is irrational?
a. 0.
b. square root of 5
c. 0.
d. 0.3
is it square root of 5?

Irrational numbers are number that can't be written in a/b form where a and b are integers and b≠0

if it repeats, it can be written as a fraction
if it terminates, it can also be written as a fraction

if you have a square root that doesn't simplify nicely, we assume it to be irrational

so

A. 0.454545=45/99
B. irrational
C. 7/9
D. 3/10

yep, it's √5