In which of the following compounds is the oxidation state of $Fe$ zero?

The following reaction is performed for detection of $NO_2^{-}$: $FeSO_4 + NO \rightarrow$ Product. Choose the correct statement.

$A$ coordination compound of cobalt contains five ammonia molecules,one nitro group,and two chlorine atoms per cobalt atom. One mole of this compound produces three moles of ions in an aqueous solution. Reaction of this solution with excess $AgNO_3$ yields two moles of $AgCl$ precipitate. What is the ionic structure of this complex?

Which of the following is a homoleptic complex?

Match List-$I$ with List-$II$:

List-$I$ (Complex)	List-$II$ (Primary valency and Secondary valency)
$(A)$ $[Co(en)_2 Cl_2] Cl$	$(I)$ $3, 6$
$(B)$ $[Pt(NH_3)_2 Cl(NO_2)]$	$(II)$ $2, 4$
$(C)$ $Hg[Co(SCN)_4]$	$(III)$ $3, 4$
$(D)$ $[Mg(EDTA)]^{2-}$	$(IV)$ $2, 6$

Choose the correct answer from the options given below:

Which of the following coordination complexes is a heteroleptic complex?