First let's see what does irrational mean.
An irrational number is any number that cannot be written as a fraction of whole numbers. The number pi and square roots of non-perfect squares are examples of irrational numbers. ... , however, is not a perfect square, and its square root, therefore, is irrational.
√2 is an irrational number since it cannot be written as a ratio of two integers.
look at the picture below to see why√2 is an irrational number
Please mark me brainliest if this helped.