Question

In which of the following compounds transition metal has zero oxidation state ?
A. $Cr{{O}_{5}}$
B. $N{{H}_{2}}.N{{H}_{2}}$
C. $NOCl{{O}_{4}}$
D. $[Fe{{(CO)}_{5}}]$

Answer 1

Hint: In order to solve this question we need to look for two things. First, we need an option in which there is a presence of transition metal and second we need to find the oxidation states and find the one compound with zero oxidation state.

Complete Step by Step Solution:
Transition metal describes the elements of the d-block. Between the s and p blocks are the components that make up the d-block. Between groups 2 and 13 of the periodic table is where this block is located. Fourth period onwards is when it begins.

Considering the definition of the transition metals we can see that in the question, only compounds of option A i.e. $Cr{{O}_{5}}$ and option D i.e. $[Fe{{(CO)}_{5}}]$has the presence of transition metal in it.

The hypothetical charge that an atom would hold if all of its links to other atoms were entirely ionic in nature is what is known as an atom's oxidation state.

So, in the case of $Cr{{O}_{5}}$we know that O carries a charge of -2. Let’s suppose the oxidation number of Cr is x. And this compound is an uncharged molecule, so the net charge on the compound is zero. Therefore, the oxidation number of Cr will be:
$x-2(5)=0$.

Solving it further,
$x-10=0\therefore x=10$ we know the oxidation state of +10 cannot exist so in this case the Cr will acquire the maximum stable oxidation state. For, Cr maximum stable oxidation state is +6. Therefore the oxidation state of Cr in $Cr{{O}_{5}}$ is +6.

Now, in the case of$[Fe{{(CO)}_{5}}]$ we know this is a coordination complex and CO is a ligand which carries a charge of 0. Let’s suppose the oxidation number of Fe is y. And this compound is an uncharged compound, so the net charge on the compound is zero.

Therefore, the oxidation number of Fe will be:
$y-5(0)=0$Solving it further,
$y=0$ Therefore the oxidation state of Fe in $[Fe{{(CO)}_{5}}]$ is 0.
Hence, the correct option is D. $[Fe{{(CO)}_{5}}]$

Note: In this question, first identify the option with the transition metal. After that, find the oxidation states with the appropriate method. If the oxidation state of any metal exceeds the maximum stable oxidation state then the oxidation state is that maximum stable state only.