White precipitate of $AgCl$ dissolves in aqueous ammonia solution due to formation of $.....$ .

$AgCl$ precipitate dissolves in ammonia due to the formation of

Identify the lowest field strength ligand from the following.

The molar ionic conductances of the octahedral complexes are in the order of:
$(1) PtCl_4 \cdot 5NH_3$
$(2) PtCl_4 \cdot 4NH_3$
$(3) PtCl_4 \cdot 3NH_3$
$(4) PtCl_4 \cdot 2NH_3$

When concentrated $HCl$ is added to an aqueous solution of $CoCl_2$,its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?

Select the most stable complex.