Answer: C - The iron becomes harder and stronger
Step-by-step explanation:
The pure iron when mixed with the carbon then steel is formed which is the interstitial alloy of iron. About 0.002%- 2.1% (m/m) of carbon. The carbon atoms being smaller than the iron atom occupy the interstitial spaces or interstices in between the iron atoms. Thus these carbon atoms introduce imperfections in the iron crystal layer. The iron crystal layers become harder and they slide past one another and the iron becomes harder.