Explanation

(a)
$NO_{2}^{-}$ can participate in linkage isomerism because it may be bonded to metal through nitrogen or through oxygen.
${\lbrack\left( NH_{3} \right)}_{5}CoNO_{2}\rbrack Cl_{2}\ \ \ and\ \ \left\lbrack \left( NH_{3} \right)_{5}CoONO \right\rbrack Cl_{2}\$
Pentaamminenitro pentaamminenitro
cobalt (III) chloride cobalt (III) chloride