Test and analysis: According to the fact that T has no positive valence, T is fluorine; Y, Z, R and T are in the same period, so in the second period, if the number of electrons in the outermost layer of R is three times that of the second outer layer, then R is an oxygen element; If the number of electrons in the outermost layer of Z is equal to the number of electrons in the second outer layer, then Z is beryllium; Y and Z are metal elements, Y is in the second period, so Y is lithium element; If X and Z are in the same main family, then X is magnesium or calcium; If X is magnesium, and the sum of the atomic numbers of X and R is twice that of W, then (12+8) ÷ 2 = 10 does not meet the question. If X is calcium, the sum of the atomic numbers of X and R is twice that of W, (20+8) ÷ 2 = A, Y is lithium, Z is beryllium, R is oxygen, T is fluorine, which is the same period, and the atomic radius of elements decreases from left to right, so A is correct; If b and w are silicon, r is oxygen, t is fluorine, nonmetal F > O > Si, and the stability of gaseous hydride is W < R < T, then b is correct; C, x is calcium and z is beryllium. If calcium is a metal, the alkalinity of the hydrate corresponding to the highest valence oxide is X > Z, so C is correct. D, XR 2 and WR 2 compounds CaO 2 and SiO 2, because calcium is +2 and silicon is +4, the valence of R is-1 and -2 respectively, that is, the valence of R in XR 2 and WR 2 compounds is different, so D is wrong, and the answer is D.