Question

If the aluminium salt of an anion X is Al2X3, what is the valency of X ? What will be the formula of the magnesium salt of X ?

Answer 1

Valency of X in the aluminium salt Al₂X₃ can be worked out as follows (we know that valency of Al is 3):

Element    Al  X
Valency     3   2
Thus, it is clear that the valency of X is two.

Formula for the magnesium salt of X can be worked out as follows:

Element  Mg  X
Valency     2    2

Crossing the valencies gives us the formula of the magnesium salt of X i.e. MgX.