AP Chemistry: 2.4 Structure of Metals and Alloys- Exam Style questions with Answer- MCQ

Ans: D

The rigidity of steel is primarily influenced by its structure and composition. In this case, the difference between low-carbon steel and high-carbon steel lies in the amount of carbon present in the alloy.

Option (D) best explains why high-carbon steel is more rigid than low-carbon steel. The additional carbon atoms within the alloy make it more difficult for the iron atoms to slide past one another. This results in a stronger and less ductile structure, leading to increased rigidity. In high-carbon steel, the carbon atoms occupy the interstitial spaces between the iron atoms, disrupting the regular arrangement and making it harder for the iron atoms to move relative to each other. This increased resistance to movement contributes to the steel’s rigidity.

Options (A), (B), and (C) are not directly related to the increased rigidity of high-carbon steel compared to low-carbon steel. While elemental carbon is indeed harder than elemental iron (option A), the hardness of the alloy is more influenced by the arrangement of carbon atoms within the steel matrix. Option (B) about density is not relevant to the rigidity of the steel, and option (C) about thermal conductivity is also not directly related to rigidity.