Which one of the following is not true?

Option A is incorrect because √2 cannot be written in simple fraction.

hence is irrational number, hence true.

option B is incorrect as it can be written in simple form hence it is a rational number

And also √b cannot be written in simple form hence it is a irrational number

Option C

As we know surd is a number in which we cant remove its square root(cube root …etc) hence cannot represent, in simple fraction hence it is irrational number

Hence C is true

Option D

D is not true as square root of every positive integer is not always irrational

For example, square root of 4 is 2 which is rational number hence D is not true.

Hence D is the answer