Ans. b (Selenium). (Ref. Harper, Biochemistry, 25th ed., 659,766)SeleniumFeaturesConstituent of glutathione peroxidaseSynergistic anti-oxidant with vitamin EEssential trace elementSelenocysteine is an L--amino acid found in a handful of proteins. As its name implies, a selenium atom replaces the sulfur of its structural analog, cysteine. The pK3 of selenocysteine, 5.2, is 3 units lower than that of cysteine. Since selenocysteine is inserted into polypeptides during translation, it is commonly referred to as the "21st amino acid."However, unlike the other 20 genetically encoded amino acids, selenocysteine is not specified by a simple three-letter codon.Trace elements TRACE ELEMENTDEFICIENCY STATESEXCESS STATES1ArsenicAcute Fatty (Yellow)liverHCCNeurologic dysfunctionGIT diseasesSkin cancerMee's linesAngiosarcoma of liverNCPF2Cadmium-Madness, paralysis agitans,3CopperGrowth failureWilson's diseaseNeutropenia CVS disordersGenu valgumMenke's kinky hair disease04ChromiumPEM, CVS diseaseArthritisDermatitisDiarroeaSeptal perforation5IodineGoiter, growth failureJod basedow phenomenonWolf chekoff phenomenon6Lead-Abdominal ColicAnaemiaBlue gum linesBasophilic stipplingConstipationConvulsionsDeliriumPeripheral neuropathy & ParalysisFailure of kidneysMetaphyseal lines7ManganeseImpaired growthAtaxiaManganese madnessParalysis agitansCVS disorders8MolybdenumGrowth failureGout bony defects Oral & esophageal carcinomaGenu valgum9Mercury-Minimota's disease Mercural erythesim (Hatter's shake)10SeleniumPEM, muscle dystrophy, CVS diseases(DCM), diarrhea, Keshan diseaseArthritis, dermatitis11AluminiumAlzheimer's diseaseOsteodystrophy12ZincNight blindnessHypogonadismImpaired wound healingAcrodermatitis enteropathicaGI irritationGrowth retardationFlaky paint dermatitis, loss of taste