On moving left to right in a period. Acidic character of oxides is increase. 3rd period element oxides. Basic ⏟Na2OMgOAmphoteric ⏟Al2O3Acidic ⏟SiO2P2O5Cl2O7
(i) Acidic character↑
(i) Atomic No↑so X have minimum Atomic No
& Z have maxima Atomic No So correct order is X<Y<Z