a) Na2O
mNa2O= 2*23u + 1*16u= 46u +16u= 62u
%Na= (2*23u÷62u)*100%= 74,2%
%O=(1*16u÷62u)*100%= 25,8%
b)
Al2O3
mAl2O3=2*27u+ 3*16u= 102u
%Al= (2*27u÷102u)*100%=52,9%
%O= (3*16u÷102u)*100%= 47,1%
