challenge: How can 1-Butyl-3-methylimidazolium tetrachloroferrate be obtained?
  
  A. From 1-butyl-3-methylimidazolium fluoride and ferric fluoride
  B. From 1-butyl-3-methylimidazolium bromide and ferric bromide
  C. From 1-butyl-3-methylimidazolium iodide and ferric iodide
  D. From 1-butyl-3-methylimidazolium chloride and ferric chloride
  Answer: 