Final answer:
The default subnet mask for a Class C IP address allows for 254 usable hosts.
Step-by-step explanation:
The default subnet mask for a Class C IP address is 255.255.255.0. The network portion of the IP address is represented by the 24 leftmost bits, while the host portion is represented by the 8 rightmost bits. With a Class C IP address, there are 256 possible values for the host portion.
However, two of these values are reserved: the all-zeros host address and the all-ones host address. Therefore, the number of usable hosts is 256 - 2, which equals 254.
So, the correct answer is option a. 254.