it sound like a fart :)
Bass clarinets play in orchestras because orchestras sometimes play pieces that are scored for bass clarinet, or have bass clarinet parts in it. One example of a piece like that is The Rite Of...
It depends entirely on the piece but usually 1 or more comonly none
Next to the Bassoons.
On the occasion a composition calls for a bass clarinet, there is only one in an orchestra.