AMAC (Media Access Control) addressis aunique identifier assigned to network interfacesfor communications at the data link layer (Layer 2 of the OSI model). A MAC address is:

Always48 bits(6 bytes) long

Represented in12 hexadecimal characters

Grouped into6 pairsseparated by colons or dashes (e.g., 00:1A:2B:3C:4D:5E)

Contains onlyhexadecimal characters (0-9, A-F)

Extract fromRené Meneses MTCNA Study Guide:

“A MAC address is a 48-bit value, represented as 6 groups of two hexadecimal digits (00 to FF). Any character outside this range is not valid. For example, 80:GF:AA:67:13:5D is invalid because ‘G’ is not a valid hexadecimal digit.”

Extract fromTerry Combs MTCNA Notes – MAC Addressing Section:

“Valid MAC addresses contain only 0-9 and A-F. A common mistake in training exams is to insert an invalid character like G or H into a MAC, which instantly makes it incorrect.”

Extract fromMikroTik Wiki – MAC Address Format Page:

“MAC addresses are six octets long and use hexadecimal format only. Hexadecimal numbers go from 0–9 and A–F. If a character appears outside that range, the address is invalid.”

Now let’s evaluate each option:

Option A: 80:GF:AA:67:13:5D❌Contains the letter"G", whichdoes not belong to the hexadecimal system. That makes this addressinvalid.

Option B: 95:B5:DD:EE:78:8A✅All characters are valid hex (9, 5, B, D, E, 7, 8, A)

Option C: 88:0C:00:99:5F:EF✅All valid characters.

Option D: EA:BA:AA:EE:FF:CB✅Hex only — valid.

Option E: 13:16:86:53:89:43✅Also valid hex — no issue.

So,Option A is the only invalid MAC address.