Final answer:
The IPv6 address '1' refers to the loopback address, which is ::1. It is used for testing within a device, similar to 127.0.0.1 in IPv4. Other types of IPv6 addresses have different starting patterns.
Step-by-step explanation:
The IPv6 address that represents the loopback address is ::1. This is akin to the 127.0.0.1 loopback address in IPv4. The loopback address is used by a device to send a message back to itself, commonly for testing and troubleshooting purposes. It's an address that allows for the internal testing of network software without actually sending packets on the network.
To clarify, the correct option is a) loopback. The IPv6 loopback address is simply a '1' after the initial zeros, which are often omitted for brevity. IPv6 link-local addresses typically start with 'fe80', multicast addresses start with 'ff', and global unicast addresses are structured differently and cover a wide range of other possible starting patterns.