In which category of music would you find a song typically sung while working?

ethnic
popular
folk
art

Folk song.

Explanation:

The tradition of singing while working has been a common theme in almost all of the world's people. Majority of the manual workers, especially in the past, sing along as a means of entertainment and instilling confidence in themselves through their songs. Likewise, the slaves in the plantations also use songs as a means of expressing themselves. These form of songs are typically known and referred as folk songs, which embodies the traditional and sometimes even the personal issues of their times.