Which data rate is uniquely supported by 802.11g radios that 802.11a radios do not support?

The data rate uniquely supported by 802.11g radios that is not supported by 802.11a radios is 11 Mbps.

802.11g operates in the 2.4 GHz frequency band and is backward compatible with 802.11b, which means it can support the same lower speeds as 802.11b. This includes data rates of 1, 2, 5.5, and 11 Mbps. On the other hand, 802.11a operates in the 5 GHz frequency band and, while it supports higher data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, it does not include support for the old 11 Mbps rate that comes from the earlier standard.

Therefore, 11 Mbps is a specific legacy data rate that remains available only to the 802.11g standard due to its design to maintain compatibility with 802.11b devices. This ensures that devices operating on older standards can still connect to networks using 802.11g, enhancing interoperability within mixed wireless networking environments.