How much of the air we breath comes from a distant volcano

The answer for #3 is c but i don't know why

What are the charges of the subatomic particles by choosing the answer from the drop down menu. protons have a (+1,0,or-1). (protons,neutrons,electrons) have a 0 charge. 3.) electrons have a (+1,0,-1)

An experimental procedure requires a 10 ml of acid to be dissolved