Which statement describes the composition of potassium chlorate, KClO3?
(1) The proportion by mass of elements combined in potassium chlorate is fixed.
(2) The proportion by mass of elements combined in potassium chlorate varies.
(3) Potassium chlorate is composed of four elements.
(4) Potassium chlorate is composed of five elements.
(1) The proportion by mass of elements combined in potassium chlorate is fixed.
(2) The proportion by mass of elements combined in potassium chlorate varies.
(3) Potassium chlorate is composed of four elements.
(4) Potassium chlorate is composed of five elements.