Hint: The IUPAC name of the compound formed in brown ring is PentaaquanitrosylIron(I)Sulphate.
The brown ring complex compound is given as
[Fe(H2O)5NO]SO4
The complex ion is [Fe(H2O)5NO]2+
Oxidation numbers of H2O is zero and NO is +1
Oxidation state of Fe is +1.
The IUPAC name of the compound is PentaaquanitrosylIron(I ) Sulphate.