Final answer:
In a /24 network, there are 254 usable host addresses, calculated by subtracting 2 (for the network and broadcast addresses) from the total number of addresses, which is 256 (2^8).
Step-by-step explanation:
The subject of this question lies within the realm of Computers and Technology, focusing on networking, specifically IP addressing and subnetting. When dealing with an IPv4 address like 117.21.67.25 with a /24 subnet mask, we're looking at a network where the first 24 bits (3 octets) are used for network identification, and the remaining 8 bits are used for host addresses.
In this subnet, the number of usable host addresses is calculated by taking 2 to the power of the number of host bits (in this case, 2^8 because there are 8 host bits in a /24 network) and subtracting 2 for the network and broadcast addresses, which cannot be assigned to hosts. This calculation gives us 256 total addresses minus 2, equalling 254 usable host addresses. Therefore, the correct answer is b) 254.