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

A nominal number is a form of data that represents categories or names rather than a value that can be used for mathematical operations. In this context, area codes and zip codes exemplify nominal numbers because they serve as identifiers for specific geographic locations or regions, but they do not convey any mathematical quantity or order. For instance, both '90210' and '12345' do not imply any actual numerical value in terms of operations; they only represent specific places.

In contrast, the other options exemplify different types of numerical concepts. The first option represents ordinal numbers that indicate a position or rank (first, second, third), while the second option consists of cardinal numbers that denote quantity (123, 456, 789). The last option, consisting of simple numerical digits (1, 2, 3), also pertains to cardinal numbers since they represent quantities. Therefore, area codes and zip codes stand out as nominal numbers due to their categorical nature, distinct from the numeric values in the other options.