Which IP address is a unicast address if a default subnet mask is used?

To answer this question, we first need to understand what a unicast IP address is. A unicast IP address is an address that is given to a single device within the network.

Now, if a default subnet mask is used, it means that the network is not divided into smaller subnetworks. The default subnet masks are as follows:

• For Class A IP addresses (1.0.0.0 to 126.0.0.0), the default subnet mask is 255.0.0.0
• For Class B IP addresses (128.0.0.0 to 191.255.0.0), the default subnet mask is 255.255.0.0
• For Class C IP addresses (192.0.0.0 to 223.255.255.0), the default subnet mask is 255.255.255.0

So, any IP address that falls within these ranges and uses the corresponding default subnet mask can be considered a unicast address. For example, the IP address 10.0.0.1 with a subnet mask of 255.0.0.0 is a unicast address.