Explanation:

An Ethernet address, commonly known as a MAC (Media Access Control) address, is a unique hardware identifier for network interfaces. Standard Ethernet MAC addresses are **$\text{48-bit}$** long, typically represented as $\text{12}$ hexadecimal digits (e.g., $\text{00:1A:2B:3C:4D:5E}$). These addresses are globally unique and assigned by manufacturers. * **Option A (64 bits):** While some identifiers use $\text{64 bits}$ (e.g., IPv6 interface IDs), standard Ethernet MAC addresses are not $\text{64-bit}$. * **Option B (48 bits):** This is the correct answer. Ethernet MAC addresses are $\text{48-bit}$ long. * **Option C (32 bits):** $\text{32-bit}$ addresses are characteristic of IPv4, which are logical network addresses, not physical Ethernet addresses. * **Option D (16 bits):** $\text{16-bit}$ addresses are too short for the global uniqueness required by Ethernet MAC addresses.