Q. Which of the following is the purest form of iron?
Answer: Wrought Iron
Notes:

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element (by mass) forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Wrought iron is the purest form of iron. It contains less than 0.25% carbon. Wrought iron, one of the two forms in which iron is obtained by smelting; the other is cast iron. Wrought iron is a soft, ductile, fibrous variety that is produced from a semi fused mass of relatively pure iron globules partially surrounded by slag. It usually contains less than 0.1 per cent carbon and 1 or 2 per cent slag. It is superior for most purposes to cast iron, which is overly hard and brittle owing to its high carbon content.