Which of the following is a rational number?

A rational number is defined as any number that can be expressed as the quotient or fraction of two integers, where the denominator is not zero. In this case, the correct choice is 0.75, which can be expressed as the fraction 3/4. This fraction represents a ratio of two integers (3 and 4), confirming that 0.75 is indeed a rational number.

On the other hand, numbers like π (pi) and e are examples of irrational numbers. They cannot be accurately represented as fractions of integers, as their decimal expansions are non-terminating and non-repeating. Similarly, √2 is also an irrational number; its decimal representation is approximately 1.414213 and continues indefinitely without repeating. These characteristics distinctly classify them as irrational, differentiating them from the rational number 0.75. Thus, among the options provided, 0.75 stands out as the only rational number.