Which of the following is a rational number?

The correct answer is D √36.

Explanation: A rational number is any number that can be expressed as a fraction or ratio of two integers. The square root of 36 is 6, which is a whole number and can be expressed as ( frac{6}{1} ), thus making it a rational number. In contrast, the square roots of 97, 14, and 18 are not whole numbers and cannot be expressed as simple fractions of integers.