We can proceed by calculating masses of elements X,Y and Z present in the molar mass of the compound
using the given percentage composition of the compound.
So mass of X present in one mole of the compound is
Since according to the formula of the comound its molecule contains 2 atoms of X ,
Now from periodic table it is found that X is nothing but Al.
Similarly mass of Y in molar mass of the compound is
As the molecule contains 3 atoms of Y,
According to periodic table it should be Si.
Now finally 9 atoms of y are present in one molecule of the comound and its mass in one mole of the compound is
Consulting periodic table we can say the element Z is Oxygen O
So the compound will have formula