An element `X` is in group 13 of the periodic table. What is the formula of its oxide?

Explanation

In order to write down the formula of the oxide of element `X` we should know its valency. The valency of group 13 elements is 3. So the valency of element `X` is 3. We already known that the valency of oxygen is 2. This gives us the following conclusions:
Element Valency
`X 3`
`O 2`
Since the valency of element `X` is 3 and that of `O` is 2, therefore, two atoms of `X` will combine with three atoms of `O` to form and oxide `X_(2)O_(3)`. Thus the formula of oxide of element `X` is `X_(2)O_(3)`.
We know that the element aluminium belongs to group 13 of the periodic table and has a valency of 3. So the element `X` of the above given problem could be aluminium.`Al` and the oxide `X_(2)O_(3)` could be actually aluminium oxide, `Al_(2)O_(3)`