Question

The valency of gold in $AuCl$ is:A. 1B. 2C. 3D. 4

Hint: The Combining Capacity of an element is called valency.The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
We all know how electrons in an atom are arranged in shells/orbitals in a specific order. Those electrons which are present in the outermost orbit of the atom are considered to be valence electrons. From the Bohr-bury scheme, we can infer that the outermost shell can contain 8 electrons at maximum for elements having atomic number less than 20.

The valence or valency of an element is a measure of its combining power with other elements when it forms a chemical compound. It can be the number of electrons an atom can gain, lose or share of an element.
The valency is equal to the valence electrons if it is for less than 4. If it is more than 4, the valency is minus the no of electrons in the outermost shell.
In Chloride $(Cl)$ it has 7 electrons in this outermost shell. So valency is 8 minus 7 electron in the outer shell Valency of Chloride is 1.
So $(Cl)$ valency is 1 it will combine one atom of $Au$. Then valency of $Au$ is also 1.

Note: One element can show Variable valency like $Au$ has two valency 1 and 3 and also for example, nitrogen forms a number of compounds with hydrogen which are as follows $N{{H}_{3}},{{N}_{2}}{{H}_{4}},{{N}_{3}}H$ in which nitrogen atoms have valences of 3, 2 and $\dfrac{1}{3}$respectively. Hence, it also shows variable valences.