According to IUPAC nomenclature sodium nitroprusside is named as

Options

A. sodium pentacyanonitrosyl ferrate (II)
B. sodium pentacyanonitrosyl ferrate (III)
C. sodium nitroferricyanide
D. sodium nitroferrocyanide

Answer

B

Explanation

NO readily forms coordination complexes with transition metla bions. These complex are called nitrosyls. `F^(2+)` and NO form the complex `[Fe(H_(2)O)_(5)NO]^(2+)` which is responsible for the colour in the brown ring test for nitrates. The color is due to change transfer. This complex formally constains `Fe (+1)` and `NO^(+)` . Its magnetic moment is approximately `3.9` BM, confirming the presence of three - unpaired electrons. Note that `NO^(+)` is a strong field ligand, thus, it reshuffles the electronic configuration:
`Fe^(+) (3d^(6) 4s^(1)) rarr Fe+ (3d^(7) 4s^(0))`
Most nitrosyl complexes are colourd. Another example is sodium nitroprusside `Na_(2)[Fe(CN)_(5)NO]` . `2H_(2)O` . The colour (brown - red) is again due to charge transfer. This complex has `NO^(+)` as a ligands and `Fe^(+)` as the central metal ion. Thus, its IUPAC name should be sodium pentacyanidonitrosonium ferrat (II). As no such option is given, we gop for second option assuming NO to be a neutral ligand.