Which of the following is an example of utility software?

Utility software is designed to help manage, maintain, and control computer resources. In this context, anti-virus software is a prime example. Its main purpose is to scan, detect, and remove malicious software (malware), thereby protecting the computer system from potential threats and ensuring optimal performance.

While an email client, spreadsheet application, and web browser are critical applications for communication, data handling, and web access respectively, they do not primarily focus on system maintenance or resource management. Thus, anti-virus software distinctly fits into the category of utility software by providing essential protection and maintenance functionalities for a computer system, which is why it is the correct choice.