The IID can be generated based on a device’s MAC address using the EUI-64 format,

• The 48-bit MAC address is split into two 24-bit segments.
• The hexadecimal value 0xFFFE
  is inserted between the two segments, expanding it to 64 bits.
• The Universal/Local (U/L) bit is inverted changing from 0 to 1 or 1 to 0 to indicate if the address is globally unique…

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Your statement about link-local addresses in IPv6 is absolutely correct.

IPv6 multicast is more efficient than broadcasting since it only sends data to specified group members instead of all devices on a network.

Devices on the same local link such as computers, switches, or routers can communicate with each other directly using Link-Local addresses without the need for a router

Global Unicast Address is in IPv6. Include its range, purpose, and how it differs from other types of IPv6 addresses.