Which of the following is NOT a valid IP address?

An IP address consists of four octets, each ranging from 0 to 255. Valid IP addresses must adhere to this rule, meaning that each segment cannot exceed 255. The address 192.168.1.256 is not valid because the last octet exceeds the maximum value allowed for any octet in an IP address.

In contrast, the other choices presented (192.168.1.1, 172.16.0.1, and 10.0.0.5) conform to IP address structure since all their octets fall within the permissible range of 0 to 255. This is why 192.168.1.256 stands out as the only invalid IP address among the options given.