(1) At the same temperature and pressure, the same volume of O2 and O3 contain the same number of molecules, that is, the molar mass ratio of O2 and O3 is 32g/mol: 48g/mol = 2: 3; The ratio of substances is 1: 1, so it is 2: 3,1:1;

(2) each ACl2 contains two Cl- s, so 1mol ACl2 contains 2mol Cl- s, so ACl2 contains 0.4mol Cl- s, so the amount of ACl2 is 0.4mol/2 = 0.2mol, so the molar mass of ACl2 is19g ÷ 0.2 mol = 95g/. The relative atomic mass of A is 95-35.5×2=24, and the element with a relative atomic mass of 24 is magnesium, so its chemical formula is MgCl2, so it is filled in: 95g/mol, 24, MgCl2;

(3)① According to the drawing, A is a condenser tube, so fill in: condenser tube;

② During distillation operation, the thermometer can't reach below the liquid level, and the water inlet should be at the bottom B, so fill in: the thermometer can't reach below the liquid level, but should reach the bottle mouth; The water inlet is above A and should be below B;

(4)① The instrument used for extraction is mainly a separatory funnel, so fill in: separatory funnel;

(2) A, the solution is layered, the upper layer is yellow, and the lower layer is purple, so A is wrong;

B, liquid separation, the carbon tetrachloride solution of iodine first flows out from the lower mouth of the funnel, and the water layer is also poured out from the upper mouth of the liquid separation funnel, so B is wrong;

C, the solubility of iodine in carbon tetrachloride is greater than that in water, so C is correct;

D, iodine does not react with carbon tetrachloride solution, so D is correct;

So fill in ab.