$AlF_3$ is soluble in $HF$ only in the presence of $KF$. This is due to the formation of:

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 complex is formed when an aqueous solution of $NH_3$ is added to a $CuSO_4$ solution,resulting in a deep blue color?

Some salts,although containing two different metallic elements,give a test for only one of them in solution. Such salts are:

Which of the following is the correct increasing order of ligand field strength according to the spectrochemical series?

Aqueous copper sulphate solution (blue in colour) gives:
$(i)$ a green precipitate with aqueous potassium fluoride,and
$(ii)$ a bright green solution with aqueous potassium chloride
Explain these experimental results.