The overall complex dissociation equilibrium constant for the complex $[Cu(NH_3)_4]^{2+}$ ion will be (given $\beta_4$ for this complex is $2.1 \times 10^{13}$,where $\beta_4$ is the association constant).

When $100 \ mL$ of $0.2 \ M$ solution of $CoCl_3 \cdot x NH_3$ is treated with excess of $AgNO_3$ solution,$3.6 \times 10^{22}$ ions are precipitated. The value of $x$ is $\left(N_A = 6 \times 10^{23} \ mol^{-1}\right)$

Identify the correct statements from the following:
$A$. $[Fe(C_2O_4)_3]^{3-}$ is the most stable complex among $[Fe(OH)_6]^{3-}$, $[Fe(C_2O_4)_3]^{3-}$ and $[Fe(SCN)_6]^{3-}$.
$B$. The stability of $[Cu(NH_3)_4]^{2+}$ is greater than that of $[Cu(en)_2]^{2+}$.
$C$. The hybridization of $Fe$ in $K_4[Fe(CN)_6]$ is $d^2sp^3$.
$D$. $[Fe(NO_2)_3Cl_3]^{3-}$ exhibits linkage isomerism.
$E$. $NO_2^-$ and $SCN^-$ ligands are $NOT$ ambidentate ligands.
Choose the correct answer from the options given below:

The active substance in Nessler's reagent used for the detection of ammonia is ..........

Assertion : Low spin complexes have lesser number of unpaired electrons.
Reason : $[FeF_6]^{3-}$ is a low spin complex.

Assign $A, B, C, D$ from the given type of reaction.
$Cr(OH)_3 \downarrow + NH_3 \text{ (excess)} \longrightarrow [Cr(NH_3)_6]^{3+}$