UPSC CAPF AC 2019 Paper

According to the question, the chemical formula of sodium salt of an anion, X is Na2X.
As we know, sodium is singly ionized atom. This means that it can loss only one electron from its ground state. So, oxidation state of sodium ion in salt is +1
So, +1 × 2 + y = 0 ⇒ y = -2
It is clear that oxidation state of anion is -2.
Now, we have to find out chemical formula of aluminium salt.
We know, oxidation state of Aluminium ion is +3
Let r, Aluminium ions compound with q anion salts.
Then,+ 3 × r + (– 2)q = 0
or, 3r = 2q
or,

r

q

=

2

3

So, the chemical formula will be A2X3