Question

Which of the following is irrational?

Answer 1

(a) $$\sqrt{\frac{4}{9}}=\frac{3}{2}$$ which is a rational number.
(b) $$\frac{\sqrt{12}}{\sqrt{3}}=\frac{\sqrt{4\times 3}}{\sqrt{3}}=\frac{2\sqrt{3}}{\sqrt{3}}=2$$ Which is a rational number.
(c) $$\sqrt{7}$$ is a irrational number.
(d) $$\sqrt{81}=9$$ which is a rational number.
Hence, (c) is the correct answer.