Question

What is the metal oxidation number in the complex ion, ${{\left[ Zn{{\left( OH \right)}_{4}} \right]}^{2-}}$ ?

Answer 1

We know that to solve this problem we have to consider the oxidation state of zinc as x and then by adding the oxidation state of the other elements which will be equal to the net charge present in the molecule.

Complete answer:
The term oxidation number could be defined as the number which provides us the information whether the given species is anionic or cationic in nature. It is a crucial factor of any given species because it also tells us about the nature or the reactive properties of that species. The oxidation number of a complex ion or a complex compound is the charge carried by that specific ion in terms of integers. It results because of the presence of extra electrons, which corresponds to negative oxidation state, or the absence of electrons, which corresponds to the positive oxidation state.
For instance, if a species possesses a negative oxidation number or state, it tells us that the species is capable of binding with the species which have positive oxidation number or state. Moreover, species which have negative oxidation numbers can also donate their electrons because of the higher abundance of electron clouds, and so they are also termed as bases, whereas in the case of the positive ions, they can be termed as acids, as they have electron attracting properties.
Here we have $Zn\left( OH \right)_{4}^{2-}$ is a complex ion in which the oxidation number of $Zn$ is $\,+II.$ Oxidation numbers of hydrogen $\left( +I \right)$ and oxygen $\left( -II \right)$ are standard. Its formation reaction: $Z{{n}^{2+}}+4H{{O}^{-}}\to {{\left[ Zn{{\left( OH \right)}_{4}} \right]}^{2-}}$Charge and mass are conserved, as in every chemical equation. The ${{\left[ Zn{{\left( OH \right)}_{4}} \right]}^{2-}}$ species is a complex ion, for which there are many examples.

Additional Information: In the given molecule the ligand which has two donor sites is known as a bidentate ligand. When a ligand has multiple sites which act as a donor atom then it forms the ring-like structure called chelate and the ligand is known as the chelating ligand which forms a stable structure. Oxidation state is the number which is assigned to an element in chemical combination which usually represents the number of electrons which are loosed or gained by that element.

Note:
Remember that the oxidation number of a compound is the total charge which is possessed by a molecule or an ion or a component of a coordination sphere. It is generated solely because of the gain of one or more than one electron or loss of it.