Which of the following tools is commonly used for network monitoring?

Wireshark is a widely recognized tool in the field of network monitoring. It is an open-source packet analyzer that enables users to capture and interactively browse the traffic running on a computer network. By capturing packets in real time, Wireshark allows network administrators and security professionals to analyze the data packets that are sent and received over the network, providing insights into network performance, security issues, and troubleshooting network problems.

The other tools mentioned, such as Photoshop, Excel, and Notepad, serve different purposes. Photoshop is primarily an image editing software, not linked to network monitoring. Excel is a spreadsheet application that can manage and analyze data but lacks the specific capabilities required for real-time network traffic analysis. Notepad is a text editor useful for writing and editing text files but does not have any functionality for monitoring networks. Hence, Wireshark stands out as the only tool specifically designed for the task at hand, making it the correct choice.