Who conducted experiments to determine the quantity of charge carried by an electron?
rutherford
millikan
dalton
thomson

it was Millikan. He conducted the oil drop experiment. Thomson determined the electon charge not the quantity. Rutherford used the gold foil experiment to find positive charge and that most of the atom is empty space. Dalton proposed that matter was made of small particles called atoms but that was a concept already proposed by ancient greeks. Dalton also proposed the atomic theory.

it means there are 3 atoms of oxygen