Question

The oxidation number of $Ni$ in $Ni{{(CO)}_{4}}$ is +2
A. True
B. False
C. Anomalous
D. None of these

Answer 1

Hint: When an element forms a bond with another element or compound, it loses or gains electrons in order to form the chemical bond. These lost or gained electrons are known as the oxidation number or oxidation state of the element.

Complete-step- by- step answer:
Let’s see the rules for calculating oxidation number
a) Any free element that has an oxidation number is zero.
b) For mono-atomic ions, the oxidation number always has the same value as the net charge corresponding to the ion.
c) In the case of neutral compounds, the sum of all the oxidation numbers of the constituent atoms totals to zero.
d) If polyatomic ions are examined, the sum of all the oxidation numbers of the atoms that aggregate them equals the net charge of the polyatomic ion.

The charge on CO group is 0 because carbon here is in +2 oxidation state and oxygen is in -2.
Considering the oxidation number of Ni is $x$.
$\begin{array}{*{35}{l}}
   x+charge\text{ }\!\!~\!\!\text{ }on\text{ }\!\!~\!\!\text{ }CO=0 \\
   x+4(0)=0 \\
   x=0 \\
\end{array}$
Thus, the oxidation number of $Ni$in a $Ni{{(CO)}_{4}}$ is zero according to the above-mentioned rules and calculations and the given statement is false.

So, the correct option is “B”.

Additional Information:
1. The hydrogen atom exhibits an oxidation state of +1. . However, when hydrogen is bonded to a less electronegative element then it has the tendency to gain electrons and shows an oxidation state of -1.
2. Oxygen has an oxidation of -2 in most of its compounds. . However, in peroxides, the oxidation number of oxygen is -1.
3. All alkali metals have an oxidation state of +1 in their compounds.
4. All alkaline earth metals exhibit an oxidation state of +2 in their compounds.

Note: Oxidation number of an element should not be confused with the charge present on the element. The oxidation number is a hypothetical number and is calculated using arbitrary rules. It becomes important only during a chemical reaction or to explain bonding.