Why does the formula for the number of hosts per subnet (2H – 2) require the subtraction of two hosts?

(A) To reserve two addresses for redundant default gateways (routers)
(B) To reserve the two addresses required for DHCP operation
(C) To reserve addresses for the subnet broadcast address and subnet ID
(D) To reserve addresses for the subnet ID and default gateway (router)

C - To reserve addresses for the subnet broadcast address and subnet ID is the correct answer. By definition, two address values in every IPv4 subnet cannot be used as host IPv4 addresses:
1. The first (lowest) numeric value in the subnet for the subnet ID.
2. The last (highest) numeric value in the subnet for the subnet broadcast address.