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.

The stepwise stability constants of a complex are given below. What is its overall reaction stability constant $\beta_4$ ?
$M + L \rightleftharpoons ML ; K_1 = 1.0 \times 10^4$
$ML + L \rightleftharpoons ML_2 ; K_2 = 1.0 \times 10^3$
$ML_2 + L \rightleftharpoons ML_3 ; K_3 = 1.0 \times 10^3$
$ML_3 + L \rightleftharpoons ML_4 ; K_4 = 1.0 \times 10^2$
(Overall reaction : $M + 4L \rightleftharpoons ML_4$)

The most stable ion is

Assign $A, B, C, D$ from the given type of reaction.
$CuSO_4 + NH_3$ (Excess) $\longrightarrow [Cu(NH_3)_4]^{2+}$

Nitrate is confirmed by the ring test. The brown color of the ring is due to the formation of: