Statement B: One of the routers has two connected serial interfaces.

This statement is true if the diagram indicates that a router has two serial interfaces. In network diagrams, routers often have multiple interfaces to connect different segments or other routers, particularly for WAN connections.

Statement E: The subnet address of PC-B has 18 bits dedicated to the network portion.

If PC-B's subnet is represented by an address such as 192.168.x.x/18, then 18 bits are used for the network portion, leaving 14 bits for host addresses. This aligns with standard subnetting practices where a /18 subnet mask means the first 18 bits define the network, and the remaining bits define host addresses.

For example, a subnet mask of 255.255.192.0 corresponds to /18 in CIDR notation, indicating that the first 18 bits are for the network portion.

Incorrect Statements:

Statement A: PC-A and PC-B are in the same subnet.

This statement can be evaluated based on the IP addresses and subnet masks provided for PC-A and PC-B. If they share the same network portion of their addresses and subnet masks, then they are in the same subnet. However, without explicit addresses, this cannot be verified.

Statement C: The subnet of PC-C can contain 256 hosts.

For a subnet to contain 256 hosts, it would need a /24 subnet mask (255.255.255.0), which provides 256 IP addresses (254 usable for hosts). The subnet mask should be examined to determine the validity of this statement.

Statement D: R1 and R3 are in the same subnet.

This depends on the IP addresses and subnet masks assigned to the interfaces on R1 and R3. If they are within the same network range, then they would be in the same subnet.

Since the network diagram is not provided, the verification is based on common networking principles and standard practices in subnetting. For detailed and accurate confirmation, the exact IP addresses, subnet masks, and interface connections need to be reviewed.