The brown ring test for $NO_2^-$ and $NO_3^-$ ions is due to the formation of which of the following complex ions?

Given below are two statements:
Statement $I$ : $N(CH_3)_3$ and $P(CH_3)_3$ can act as ligands to form transition metal complexes.
Statement $II$: As $N$ and $P$ are from same group,the nature of bonding of $N(CH_3)_3$ and $P(CH_3)_3$ is always same with transition metals.
In the light of the above statements,choose the most appropriate answer from the options given below:

Arrange the ligands $NH_3, en, Cl^-,$ and $CO$ in the increasing order of their field strength (spectrochemical series).

Assign $A, B, C, D$ for the type of observation in the following reaction:
$CuSO_4 + KCN \text{ (excess)} \longrightarrow K_3[Cu(CN)_4] + \frac{1}{2}(CN)_2$

The correct increasing order of trans-effect of the following species is:

Identify the ligand with the highest field strength among the following.