Question

The oxidation number of $Ni$ in $Ni{(CO)_4}$ is $+ 2$
A) True
B) False
C) Anomalous
D) None of these

Answer 1

The given compound is a coordination compound. Coordination compounds are the one which contain one or more metal atoms which are bonded to one or more ligands. The ligands donate its electrons to the metal atom. We know that this compound does not contain any charge so the overall charge of this compound will be zero.

Complete step by step answer:
According to Werner's coordination theory, two types of valency are present which are known as the primary valency and the secondary valency. The primary valency is the number of negative ions which are equivalent to the charge on the metal ion. The primary valency is basically the oxidation number of the metal ion.
On the other hand, the secondary valency is the number of ions or molecules(ligands) that are coordinated to the metal ion. This is also known as the coordination number of the metal ion.
We know that $CO$ is a neutral ligand, so the charge on it will be $0$ and since four $CO$ ligands are bonded with the nickel atom (central atom) hence it will be multiplied by four.
Let $x$ be the oxidation state of nickel in the complex $Ni{(CO)_4}$
So,
$x + 0 \times (4) = 0 \\\ x + 0 = 0 \\\ x = 0 \\\$
Hence the oxidation number of $Ni$ in $Ni{(CO)_4}$ is $0$
So, the correct answer is Option B. i.e. False.

Note: Generally, coordination compounds are neutral compounds. By looking at the number of ligands attached to the central metal atom we can easily determine the coordination number of the central metal. Here the coordination number of $Ni$ in $Ni{(CO)_4}$ is $4$ , as four carbonyl ligands are attached to it.