Which of the following is an example of a rational number?

A rational number is defined as a number that can be expressed as a fraction or ratio of two integers, where the denominator is not zero. In this case, 1/3 is a perfect example of a rational number because it is formed by dividing the integer 1 by the integer 3.

Both the numerator (1) and the denominator (3) are integers, and since 3 is not zero, this fraction is valid. Additionally, rational numbers can also include whole numbers and integers, as they can be expressed as a fraction (for instance, 4 can be written as 4/1).

The other examples mentioned do not meet this criterion. The square root of 2 is an example of an irrational number because it cannot be expressed as a fraction of two integers; it is a non-repeating, non-terminating decimal. Similarly, π (pi) and e (the base of the natural logarithm) are also irrational numbers because they cannot be represented as exact fractions of integers, and their decimal representations are non-repeating and infinite. Thus, among the provided options, 1/3 is distinctly a rational number.