Which device interface IP address should be used as the default gateway setting of host H1?

The default gateway of a host is the IP address of the router interface that is used for communication outside the local subnet. In this scenario, host H1 would require the IP address of the router interface that provides connectivity to other networks, typically the interface on the router that is within the same subnet as H1.

The choice R1: G0/0 indicates a router interface that is directly connected, making it a suitable default gateway for hosts within the same IP range. When H1 needs to send packets to a destination outside its local subnet, it forwards these packets to R1: G0/0. This will ensure that H1 can effectively communicate with devices on different networks, as R1 will receive and appropriately route the traffic.

The other options suggest router interfaces that may not be in the same subnet as H1 or serve different network roles, and thus, would not be valid as default gateway addresses for H1. The correct setup is crucial for ensuring that host traffic is managed effectively and can reach its intended destinations across interconnected networks.