The set of numbers that is always rational is integers.
Rational numbers are defined as numbers that can be expressed as the quotient of two integers (where the denominator is not zero). Since integers are whole numbers (including positive, negative, and zero), they can all be expressed as a fraction with a denominator of 1, making them rational.
In contrast, real numbers include irrational numbers as well, decimals can be both rational and irrational, and positive numbers can also include irrational values.