Question

The ion that is not univalent is
A. Ammonium
B. Sodium
C. Bicarbonate
D. Sulphite

Answer 1

Hint: We can define valency as the total of electrons which are gained or lost by an atom to control the steadiness for getting the electronic configuration of the noble gas which is adjacent to the element. We can conclude the valency using the octet rule, with the help of a periodic table and also based on the chemical formula.

Complete step by step answer:
We can say valency is the capability of atoms of a single element to react and join with a particular number of atoms of another element.
Based on the valency, we can classify ions as,
1,Univalent: Ions that contain one charge. Example: Cesium cation
2.Bivalent: Ions that contain two charges. Example: Magnesium cation
3.Trivalent: Ions that contain three charges. Example: Aluminum cation
4.Polyvalent: Ions that contain many variable charges. Example: Iron (Seen as +2 and +3 ions.
From the above explanation, we saw that univalent means ion that contains a single charge. Let us now identify the ion that is not univalent.
Ammonium is an example of an univalent ion that contains ${\text{ + 1}}$ charge. Therefore, the option (A) is incorrect.
Sodium is an example of an univalent ion that contains ${\text{ + 1}}$ charge. Therefore, the option (B) is incorrect.
Bicarbonate is an example of an univalent ion that contains ${\text{ + 1}}$ charge. Therefore, the option (C) is incorrect.
Sulphite is an example of bivalent ion as it contains ${\text{ - 2}}$ charge. Therefore, the option (D) is correct. We can draw the structure of sulphite as,

So, the correct answer is Option D.

Note: We have to remember that the difference between the octet and the total of valence electrons would also give the valency of an element. We know that the valency is the total of electrons that is required to finish its octet. We know that the octet rule says that the valence shell of an atom is filled with eight electrons then the atom is said to be most stable.