Which of the following is considered a legal use of amateur radio frequencies?

Conducting emergency communications is considered a legal use of amateur radio frequencies because one of the primary purposes of amateur radio is to assist in emergencies. Ham radio operators often provide essential communication services during disasters or public emergencies when other forms of communication may be down or overwhelmed. This capability is rooted in the tradition of amateur radio operators stepping up to support their communities.

Amateur radio is specifically designated for personal, non-commercial communication, hampering uses like commercial broadcasting or transmitting music, which are reserved for licensed services. Operating without a license is also illegal; amateur operators must hold an appropriate license to use these frequencies legally, thereby ensuring they meet the necessary standards and regulations set by the governing bodies.