Question

What is the IUPAC name of ${{K}_{3}}[Fe{{(CN)}_{5}}NO]$?

Answer 1

While naming a coordination compound, the oxidation state of the central metal ion is always mentioned in brackets, in roman at the end of the name of metal.
The coordination sphere could be positive or negative, and the names of the substituent changes in both the cases, in order to differentiate the two.

Complete answer:
IUPAC nomenclature stands for the International Union of Pure and Applied Chemistry. IUPAC naming used for organic and inorganic compounds is a systematic way of naming, by the use of certain specific rules. These specific rules are mentioned below.
At the beginning we identify the longest carbon chain. This longest carbon chain identified by us, is termed as the parent chain.
In the next step we identify all of the substituents in this parent chain which are attached through bonds. We would term them as functional groups.
Now in the next step, we number the carbons which are present in the parent chain which is the longest chain, from that end which provides the lowest numbers to the substituents attached to the main chain. If two or more than two side chains acquire the equivalent positions, assigning the lowest number in accordance with the alphabetical order, as in the functional group whose name comes up first according to the alphabet, would be numbered first.
If the same functional group comes up more than once, we would write the location or the number of positions of each carbon on which the functional group is attached. Also, we would mention the number of times that functional group is coming up, by using a prefix (di, tri, tetra, etc.).
If in any case there are two or more than two distinct functional groups, they would be mentioned in an alphabetical order by the use of the name of the base. Some prefixes such as sec- and tert- should not be used in determining the alphabetical order.
If we consider the question, the IUPAC name of ${{K}_{3}}[Fe{{(CN)}_{5}}NO]$ would be Potassium pentacyano nitrito $-N-$ ferrate $(III)$.

Note: The nitrile or the $-CN$ group becomes cyano when it is present in the negative ion part of a coordination compound. Here in case of ${{K}_{3}}[Fe{{(CN)}_{5}}NO]$, the coordination sphere is negative so the $-NO$ part also becomes nitro, while naming.
The word root -pent, represents five, as five cyano groups are present in the coordination sphere and the oxidation state of the iron, or the central metal is always mentioned in the brackets in roman numeric.