Explanation

(b)
IUPAC name of sodium nitroprusside ${Na}_{2}\lbrack Fe(CN)_{5}NO\rbrack$ is sodium pentacyanonitrosyl ferrate (III) because in it NO is neutral ligand and the oxidation number of Fe is III, which is calculated as
2$\times$ON of Na+ ON of Fe +5$\times$ON of CN
+1$\times$ON of NO=0
2$\times$(+1)+ON of Fe +5$\times$ (-1) +1$\times$0=0
ON of Fe =5-2=+3