Final answer:
To meet the requirement of 12 subnets with a minimum of 12 hosts each in a Class C network using a single mask, a /28 mask (255.255.255.240) should be used. This provides 16 subnets, each with the capability of accommodating 14 usable host addresses, which is sufficient for the largest subnet's need.
Step-by-step explanation:
The student's question pertains to designing an IP subnet plan for 12 subnets with the largest subnet accommodating a minimum of 12 hosts. To determine the appropriate subnet mask to use for a Class C network where a single mask must be used throughout, we need to calculate the mask that can support at least 12 hosts per subnet and also provide enough subnets for the requirement.
For a subnet to support a minimum of 12 hosts, we need to consider that each subnet has 2 addresses that cannot be used for hosts (network and broadcast addresses), so at least 14 addresses per subnet are needed. The closest number that fulfills this and is a power of two is 16 (2^4), which requires 4 bits for host addresses.
Since a Class C network has 24 network bits and we need 4 bits for the hosts, this leaves us with 4 bits for subnetting (32-24-4=4). With those 4 bits, we can create 16 subnets (2^4), which is sufficient for the requirement of 12 subnets.
Therefore, the subnet mask that can be used for this situation is a /28 (255.255.255.240) because this mask provides 16 subnets, each with 16 addresses, 14 of which can be used for host IPs.
Among the options provided, /28 is the correct subnet mask to meet the requirements of having 12 subnets with a minimum of 12 hosts per subnet.