Which of the following is NOT a valid MAC Address?

A MAC address, which is used to identify network interfaces at the data link layer of a network, is composed of six pairs of hexadecimal digits. Hexadecimal digits range from 0 to 9 and A to F, where A through F represent the decimal values 10 through 15.

In the provided choices, the first choice includes the characters "G" and "F". While "F" is valid in a hexadecimal context, "G" is not. This makes the first option invalid as a MAC address since it contains an incorrect character.

On the other hand, the other choices consist solely of valid hexadecimal characters (0-9 and A-F), each correctly formatted in pairs, which means they adhere to the specification for MAC addresses. Therefore, the first option is the only one that does not represent a valid MAC address.