Final answer:
From the list, the unpitched percussion instruments are the drum kit and bass drum, as they are membranophones used for rhythm and do not produce specific pitches. The xylophone is not an unpitched instrument, and while the triangle is unpitched, it is an idiophone.
Step-by-step explanation:
The instruments that belong to the unpitched percussion group are those that do not produce a specific pitch when struck. These are generally rhythm instruments used to maintain the tempo and add texture to the music. According to the classification system used in ethnomusicology, unpitched percussion instruments can fall under the categories of membranophones, such as a drum, which has a membrane, and idiophones, which are self-sounding instruments.
From the provided options, the drum kit and the bass drum are classified as membranophones because they consist of a skin or synthetic membrane stretched over a hollow body. On the other hand, while the xylophone is a percussion instrument, it is a pitched instrument because it has wooden bars tuned to specific notes and hence does not belong to the unpitched percussion group. Lastly, the triangle is an idiophone and, like the drum kit and bass drum, it is considered an unpitched percussion instrument.
Therefore, the instruments from the given list that belong to the unpitched percussion group are the drum kit (1) and the bass drum (4).