Question

The purest form of iron is:
A. Cast iron
B. Wrought iron
C. Pig iron
D. None of these

Answer 1

Hint: Think about the uses of all the types of iron that are mentioned in the options. Also consider what the words mean metallurgically. The process after which all these types of iron are extracted will give you an idea of their purity.

Complete step by step answer:
We will look at the types of iron mentioned in the options one by one to determine after which processes, they are extracted and the amount of impurities present in each of them.
- Cast iron
It is a type of iron-carbon alloy that contains about 2-4% impurities that consist chiefly of carbon. Silicon, manganese, phosphorus, and sulphur may also be present in trace amounts. It is obtained by melting pig iron or smelting iron ore in a blast furnace. Cast iron is mainly used to make utensils. Cast iron basically means that it is given shape by ‘casting’ the molten iron into a mould. The fact that it is an alloy contributes to its low melting point and helps in the moulding.
- Wrought iron
This type of iron contains less than 1% of slag and impurities. It is usually given shape by using its property of malleability and ductility. It is obtained after extensive purification of the iron ore. It is obtained by puddling pig iron while it is molten. The impurities present are mostly fibrous in nature and give the wrought iron its texture.
- Pig iron
This type of iron is obtained by smelting iron ore in a furnace. It is also the first form of crude iron that is obtained. The name itself suggests that it has a lot more impurities than cast iron and wrought iron since they are obtained by processing pig iron. So, we can rule out this option among the answers.
According to all the information that is given and observing their carbon content and usage. We can say that wrought iron is the purest form of iron. Hence, the correct option is ‘B. Wrought iron’.

Note: Even if it seems that cast iron and wrought iron seem similar in their impurity content, the impurities in wrought iron are filamentous in nature and are added to specifically contribute to the texture of the iron. On the other hand, the impurities in cast iron are present because they cannot be removed.