Consider three machines M, N, and P with IP addresses 100.10.5.2, 100.10.5.5, and 100.10.5.6 respectively. The subnet mask is set to 255.255.255.252 for all the three machines. Which one of the following is true?

To determine which machines belong to the same subnet, we perform a bitwise AND between each IP address and the subnet mask $255.255.255.252$ (a $/30$ mask with a block size of $256 - 252 = 4$ addresses per subnet).

Looking at the last octet:

• For Machine M ($100.10.5.2$):

  $$\text{Subnet ID} = 2 \text{ AND } 252 = 0 \implies 100.10.5.0/30$$

  Usable IP range: $100.10.5.1$ to $100.10.5.2$.

• For Machine N ($100.10.5.5$):

  $$\text{Subnet ID} = 5 \text{ AND } 252 = 4 \implies 100.10.5.4/30$$

  Usable IP range: $100.10.5.5$ to $100.10.5.6$.

• For Machine P ($100.10.5.6$):

  $$\text{Subnet ID} = 6 \text{ AND } 252 = 4 \implies 100.10.5.4/30$$

  Usable IP range: $100.10.5.5$ to $100.10.5.6$.

Thus, only N and P belong to the same subnet ($100.10.5.4/30$), whereas M belongs to a different subnet ($100.10.5.0/30$).

Therefore, option (C) is correct.