To support about 800 workstations with minimal IP waste, you choose the smallest subnet that provides at least 800 usable host addresses. In IPv4, usable hosts per subnet are calculated as 2^(host bits) # 2 (subtracting network and broadcast addresses). A /22 leaves 10 host bits (32 # 22 = 10), providing 2^10 # 2 =
1024 # 2 = 1022 usable addresses-enough for 800 devices with relatively low waste.
Check the other options: /23 leaves 9 host bits, giving 2^9 # 2 = 512 # 2 = 510 usable addresses, which is not enough. A /21 provides 2^11 # 2 = 2048 # 2 = 2046 usable addresses-enough, but wastes more than /22. A
/20 provides 2^12 # 2 = 4096 # 2 = 4094 usable addresses-much more waste.
Therefore, 10.0.100.0/22 is the best choice that meets the workstation requirement while minimizing unused addresses.