bass
Timbre
Typically, a group of three instruments or voices is called a trio or a triad. In some rare, informal atmospheres, they are also called tritets, but this almost never happens in a classroom or professional setting.
A piece of music for eight voices or eight instruments would be called an octet. Some noted octets have been written by Beethoven, Mendelssohn, Schubert, Stravinsky, and Steve Reich.
The treble clef or the G clef they are both the same thing
The distance between the lowest and highest tones that a voice or instrument can produce is called the "range." For voices, this is typically measured in octaves, and ranges can vary significantly among different types of voices (soprano, alto, tenor, bass). Instruments also have specific ranges depending on their design and construction. The wider the range, the more versatile the voice or instrument is in producing varied musical notes.
No instruments are used in a Cappella, only your voices.
no
They can be both high and low pitch. There are brass instruments that are considered "high voices" like trumpets, there are brass instruments that are considered "middle voices" like french horns, and then there are brass instruments that are considered "low voices" like trombones, euphoniums, and tubas. All brass instruments have a pretty large range of pitches they can play depending on how good the player is, so the pitches can greatly vary.
song
The lowest part in early polyphony is called the tenor voice. It provided the foundation and support for the higher voices in the musical texture, typically sung by male singers. The tenor voice often carried the cantus firmus or melody.
There's a small trumpet called a piccolo trumpet which sounds one octave higher than a regular trumpet, and nearly always has four valves to aid in fast fingering. One is used for the famous song Penny Lane by the Beatles. It has a great ability to sound clear and bright above the midrange instruments and voices. If there's any other brass instrument that's even higher in range, it's something rare, experimental or a novelty.
Octet