Write the formulae of the following compounds, showing the steps involved.

(a) sodium oxide
(b) magnesium nitrate
(c) magnesium sulphate
(d) aluminium chloride

Let's write the formula of the given compounds along with the steps involved.
a. Sodium oxide
* The elements in sodium oxide are sodium and oxygen. The valency of sodium is 1 and oxygen is 2. Therefore, we write the symbols as Na₁ and​ O₂.
* The common factor among the numbers 1 and 2 is nil.
* The valencies are exchanged and are written as subscripts to the elements. Thus, the formula of sodium oxide would be Na₂O.


b. Magnesium nitrate
* Magnesium nitrate contains the element magnesium and nitrogen. The valency of magnesium is 2 and radical of nitrogen is 1. Therefore, we write the symbols as Mg₂ and (NO₃)_1.
* The common factor among the numbers 1 and 2 is nil.
* The valencies are exchanged and written as superscripts to the elements. As the radical contains more than 2 atoms, the radical is written in brackets and the exchanged valency is written as its subscript. Thus, the formula of magnesium nitrate would be Mg (NO₃)₂.


c. Magnesium sulphate
* Magnesium sulphate contains the element magnesium and sulphur. The valency of magnesium is 2 and that of the radical of sulphur is also 2. Therefore, we write the symbols as Mg2 and ​(SO4)₂.
* The common factor among the numbers 2 and 2 is one.
* As both the element and radical’s valencies are one, neither the radical will not be written in brackets nor the valency number will be written as a subscript. Thus, the formula of Magnesium sulphate would be MgSO₄.


d. Aluminium chloride
* The elements in aluminium chloride are aluminium and chlorine. The valency of aluminium is 3 and chlorine is 1. Therefore, we write the symbols as Al₃ and ​Cl₁.
* The common factor among the numbers 1 and 3 is nil.
* The valencies are exchanged and are written as subscripts to the elements. Thus the formula of aluminium chloride would be AlCl₃.