Assume that the IPv6 address of GE0/0/0 on R1 is 2001:db8:12::1/64.

An IPv6 solicited-node multicast address is automatically derived from the lower 24 bits of a unicast or anycast IPv6 address. The fixed solicited-node prefix is FF02::1:FF00:0/104. The interface address in the question is 2001:db8:12::1. Its final 24 bits are 000001 in hexadecimal representation. Combining those 24 bits with the solicited-node multicast prefix produces FF02::1:FF00:1. This multicast address is used by IPv6 Neighbor Discovery for functions such as address resolution and Duplicate Address Detection, reducing the need to disturb every host on the local link in the way an IPv4 ARP broadcast does. FF02::1 is the all-nodes link-local multicast address and FF02::2 is the all-routers link-local multicast address, so neither represents the solicited-node group for this interface. Option A contains unrelated lower-order bits and does not correspond to the source address. Therefore the derived solicited-node multicast address is FF02::1:FF00:1, making option C correct.