Which wireless standard operates at both 2.4 GHz and 5 GHz frequencies?

The standard that operates at both 2.4 GHz and 5 GHz frequencies is 802.11n. This wireless standard, introduced in 2009, supports multiple-input multiple-output (MIMO) technology, which enhances the data throughput and range compared to its predecessors. By utilizing both frequency bands, 802.11n provides improved network performance and flexibility, allowing for better compatibility with a variety of devices.

In contrast, the other standards mentioned are limited to specific frequencies. For instance, 802.11g operates only at 2.4 GHz and is known for its backward compatibility with 802.11b, but it does not provide the broader frequency range that 802.11n offers. Similarly, 802.11b is also confined to the 2.4 GHz band and does not utilize the 5 GHz spectrum at all. Lastly, while 802.11ac primarily works at the 5 GHz band, it does not support 2.4 GHz operation. Thus, 802.11n stands out for its dual-band capabilities, making it the correct choice in this context.