Final answer:
To check a network card's functionality, the technician should use the loopback address, which is 127.0.0.1. This address tests the card and the network stack of the operating system, but not connectivity to other devices.
Step-by-step explanation:
A technician seeking to verify the functionality of a network card in a client's machine should use the IP address 127.0.0.1 for this purpose. This address is known as the loopback address and is used to test the network card without the need for external network connectivity. Pinging the loopback address ensures that the operating system's network stack is operational. It does not, however, test the connectivity between different devices on the network or the reachability of a specific client machine. For that, one of the other IP addresses would be more appropriate, depending on the network configuration.
For example, the IP address 10.76.0.1 could represent a client on the same subnet, and 192.168.0.1 might be the default gateway, both of which could be used for further connectivity tests. The address 255.255.255.0 represents a subnet mask, which is not suitable for pinging as it is used to define the network's size.