Which of the following is an appropriate use of instant messaging in a professional setting?

In a professional setting, using instant messaging to log off before attending a meeting is appropriate because it communicates your status and helps manage expectations. When you notify colleagues that you are logging off, you are being transparent about your availability and ensuring they know you will not be reachable during that time. This form of communication fosters clarity and professionalism, aligning with effective workplace etiquette.

The other options do not align with professional communication standards. Starting a casual greeting might not be unsuitable, but it lacks the direct utility of logging off to inform others of your status, which is crucial in a workplace context. Snooping on a colleague's private messages is unethical and a violation of privacy, and interrupting a colleague who is busy with new messages can be disruptive and disrespectful to their workflow. Therefore, maintaining professionalism in communication is essential, and logging off thoughtfully fits that criterion.