Which of the following frequency ranges is most suited for meteor-scatter communications?

Explanation

Scatter from a meteor trail is useful only where the trail's electron density is high enough to return the signal but the frequency is above the range that ordinary ionospheric propagation already covers, and that window runs from about 10 metres through 2 metres, with 6 metres the most productive. The two HF choices are dominated by normal sky-wave propagation, and above roughly 150 MHz the returns become too weak and too brief to work.