Discuss briefly,giving an example in each case,the role of coordination compounds in:
$(i)$ biological systems
$(ii)$ medicinal chemistry
$(iii)$ analytical chemistry
$(iv)$ extraction/metallurgy of metals

(N/A) $(i)$ Biological systems: Chlorophyll,the pigment responsible for photosynthesis,is a coordination compound of magnesium. Haemoglobin,the oxygen-carrier in human blood,is a coordination compound of iron.
$(ii)$ Medicinal chemistry: Coordination compounds like $cis-platin$ (a platinum complex) are used as anti-cancer agents to inhibit the growth of tumours.
$(iii)$ Analytical chemistry: Coordination compounds are used in the detection of metal ions during salt analysis. For example,$Ni^{2+}$ ions are detected by the formation of a red precipitate with dimethylglyoxime $(DMG)$.
$(iv)$ Extraction/metallurgy of metals: Metals are extracted from their ores via complex formation. For example,gold is extracted from its ore by forming a cyano-complex $[Au(CN)_2]^-$,from which gold is later recovered by displacement with zinc.