MAC addresses are _____________ bits in length.

16 bits is far too short for a MAC address - this length is used for other protocol fields such as EtherType or VLAN tags, not hardware addresses.

24 bits represents only the OUI (vendor) portion of a MAC address, which is the first half - a complete MAC address requires all 48 bits.

32 bits is the length of an IPv4 address, which operates at Layer 3 - MAC addresses operate at Layer 2 and are physically twice this length.

A MAC address is 48 bits in length, represented as 12 hexadecimal digits. The first 24 bits form the Organizationally Unique Identifier (OUI), which the IEEE assigns to the network interface manufacturer, and the remaining 24 bits are a unique device identifier assigned by that manufacturer - together ensuring global uniqueness at the Layer 2 hardware addressing level.

64 bits is the EUI-64 identifier length used in IPv6 interface ID generation, which is derived from a MAC address by inserting 'FF:FE' in the middle - it is not the MAC address itself.