[Golden_luck]

An element X forms two oxides containing 77.47% and 69.62% of X respectively. If the first oxide has the formula XO, what is the formula of the second oxide?

[DrCMS]

Take a nominal weight of material say 100g.
Calculate how much X and O are present for each oxide as g.
Knowing the ratio is 1:1 for the first oxide and the weight of O is 16 calculate the molecular weight of X
From the weights of X and O in the second oxide with the molecular weight of X from above calculate the mole ratio for the second oxide.
Adjust the ratio to whole numbers and that is the formula for the second oxide.