Why have 900 megahertz (MHz) Industrial, Scientific, and Medical (ISM) band wireless local area networks (WLAN) lost favor compared to 2.4 gigahertz (GHz) and 5 GHz frequency systems?

The choice indicating that 900 MHz ISM band WLANs are more expensive and provide slower data throughput is correct because the 900 MHz frequency generally suffers from limitations in terms of available bandwidth compared to the 2.4 GHz and 5 GHz bands. While lower frequencies can penetrate obstacles better, which can offer some advantages in terms of range and reliability, they do not support the faster data rates that users expect in modern wireless networking. As a result, many network deployments have shifted towards using higher frequencies like 2.4 GHz and 5 GHz, which can accommodate higher data rates, support more channels, and ultimately deliver a better user experience.

In contrast, the other options are inconsistent with these characteristics. The affordability and speed of 900 MHz systems do not compete with the higher-frequency systems, and while they might be perceived as having longer ranges, the data throughput limitations diminish their attractiveness. Additionally, power efficiency is generally better associated with the newer 2.4 GHz and 5 GHz systems, which leverage more advanced technologies and standards to minimize power consumption while maximizing performance.