Final answer:
Workstation2 uses the IP address of the router interface on the same network segment as its default gateway when sending an IP packet to Workstation3.
Step-by-step explanation:
When Workstation2 sends an IP packet to Workstation3, the default gateway's IP address that is used is the IP address of the router interface that is on the same network as Workstation2. The default gateway is a router's interface that provides the access point for Workstation2 to send packets to devices on different subnets or networks. In this setup, Workstation2 would look at its own IP configuration, determine that the destination IP address (Workstation3) is not within the same subnet, and thus send the packet to the default gateway, where the router will then forward it to the correct destination.
Each device on the network that needs to communicate outside its local subnet will have a default gateway configured, typically the router's interface address on their local subnet. To find the default gateway address for Workstation2, you would check its network settings to see what IP address is configured as the gateway.