How is a rational number defined?

A rational number is defined as any number that can be expressed in the form of a fraction p/q, where p and q are integers and q is not zero. This definition encompasses a wide range of numbers, including integers (which can be expressed as fractions with a denominator of 1) and fractions themselves. The key aspect of rational numbers is that they can always be represented in this fractional format, highlighting their property of being expressible as a ratio of two integers.

The other options do not capture the complete definition of rational numbers. For instance, while finite decimal expansions are characteristic of some rational numbers (and also of terminating decimals), not all rational numbers meet this criterion. Additionally, whole numbers form a subset of rational numbers, but the definition is broader. Finally, the option describing numbers that cannot be expressed as a fraction directly points to irrational numbers, which fall outside the category of rational numbers. Thus, understanding the nature of rational numbers involves recognizing their representation as ratios of integers.