How many usable hosts are available given a class c ip address with the default subnet mask?

Class C networks have a 24 bit netmask. There are 32 bits in an IPv4 address, so 8 bits are available for node numbers. 2^8 = 256, which can be expressed as 0 - 255. The zero'th node number is the network number. The number with all bits set (255) is the broadcast address for this subnet. One of the hosts will need to be a router so that this network can communicate with other networks.