Question

If an element has a valency of 3, then find out the formula of its chloride and sulphide.
[2 Marks]

Answer 1

Let the chemical symbol of the element be X.
The valency of X is 3.

Formula of the chloride of X:

Symbol	X	Cl
Valency	3	1

Upon criss-crossing the valencies, we get the formula of the compound as $X{Cl}_3$.
[1 Mark]

Formula of the sulphide of X:

Symbol	X	S
Valency	3	2

Upon criss-crossing the valencies, we get the formula of the compound as $X_2{S}_3$.
[1 Mark]