The default subnet mask for a Class B network is 255.255.0.0. The network ID for a Class B network takes up the first two octets (16 bits) and the remaining two octets (16 bits) are used for host addressing.
The broadcast address is the address at which all hosts on the network can receive a message simultaneously. To calculate the broadcast address, we set all host bits to 1s. For a Class B network, the host bits are in the last two octets (16 bits).
Therefore, the broadcast address for a Class B network with a default subnet mask would be 172.16.255.255. So, the correct option is (c) 172.16.255.255.