Final answer:
The last 28 bits of an IPv6 multicast address uniquely identify the group ID.
Step-by-step explanation:
In IPv6 multicast addresses, the group ID is uniquely identified by the last 28 bits of the address. These 28 bits are divided into two parts: the flag bits and the scope bits.
The first 8 bits of the last 28 bits are the flag bits, which are used to specify the type and format of the multicast address. The remaining 20 bits are the scope bits, which define the scope of the multicast group.
For example, in the multicast address ff02::1:ff00:1234, the last 28 bits are 1:ff00:1234 and they uniquely identify the multicast group.