A, the more electron layers, the greater the radius, the greater the number of atoms and the smaller the radius when the electron layers are the same, and S and Cl are in the same period, so the radius S > Cl, O is the last periodic element, so the radius S > Cl > O, so A is wrong;

B, in the same period, the metallicity weakened from left to right, and the reducibility gradually weakened, so the reducibility: Na > Mg > Al, so B is correct;

C, the nonmetallic property of the same family is weakened from top to bottom, and the stability of hydride is weakened, so the stability: HF > HCl > HBR, so C is correct;

D, the stronger the nonmetallic property, the stronger the acidity of the highest valence oxyacid, and the nonmetallic property increases from left to right in the same period, so the acidity is: hclo4 > H2SO4 > h3po4, so d is correct;

So choose a.