Which among the following is the strongest ligand?

Copper sulphate solution reacts with $KCN$ to give

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?

Which of the following complexes will be the most stable?

Which of the following will $NOT$ give the characteristic test for $Fe^{2+}$ or $Fe^{3+}$ ions?

The purple color of $KMnO_4$ is due to which of the following?