Which of the following ligands can form both high-spin and low-spin complexes?

Which among the following cations will form the lowest stability complex if the ligand remains the same?

The molecular formula of a cobalt coordination complex contains five ammonia molecules,one nitro group,and two chlorine atoms for one cobalt atom. In an aqueous solution,one mole of the substance produces $3$ moles of ions. Upon reacting this solution with an excess of silver nitrate solution,$2$ moles of $AgCl$ precipitate are obtained. What is the ionic formula of the complex?

What is the color of a cobalt chloride solution?

Identify the correct decreasing order of stability of complexes formed by divalent metal ions with the same ligand.

Given the following reactions:
$Ag^{+} + NH_3 \rightleftharpoons [Ag(NH_3)]^+ ; K_1 = 1.6 \times 10^3$
$[Ag(NH_3)]^+ + NH_3 \rightleftharpoons [Ag(NH_3)_2]^+ ; K_2 = 6.8 \times 10^3$
What is the formation constant for $[Ag(NH_3)_2]^+$?