Question

valency of an element X is 3 . write the chemical formula of its oxide

Answer 1

To write its Formula,
We know valency of oxygen is 2.

And said element is 3 .

X. O
3. 2.

X2O3

Is the answer.

Hope that helps.

Answer 2

valency of element X = 3
The chemical formula of its oxide =?
Now, the valency of oxide = 2
Therefore the formula of its oxide will be X2O3