Explanation

(a)
Linkage isomerism is shown by those complexes which have an ambidentate ligand such as ${NO}_{2}^{-},\ {CN}^{-}\ and\ SC\overline{N}\ etc.\ In\ \lbrack Fe\ \left( {NO}_{2} \right)_{3}{Cl}_{3}\rbrack,\ N\ is\ donor\ atom\ while\ in\ \lbrack Fe(ONO)_{3}{Cl}_{3}\rbrack,O\ is\$donor atom.