Which example illustrates the concept of conversion?

The example of "google" as both a noun and a verb illustrates the concept of conversion, which refers to the process of changing the function of a word without altering its form. In this case, "google" originally functions as a noun, the name of a search engine, but it has also been adopted as a verb, meaning to search for information online using the Google service. This change in grammatical function from noun to verb showcases conversion effectively.

The other options represent different linguistic processes. For instance, the transformation of "happy" to "unhappy" involves the addition of a prefix, which is a process known as affixation. Similarly, combining "world" and "music" to form the compound "world music" is an example of compounding. Finally, the borrowing of "pizza" into English signifies the process of loanword adoption from another language, rather than a change in the word's grammatical function.