Correct Option
The correct option is (a).
Explanation
Stainless steel is an alloy of iron designed primarily to resist corrosion and oxidation. Unlike ordinary steel, it contains specific alloying elements that alter its chemical properties to prevent rusting.
Statement-wise Analysis
- Statement 1 is Correct: Iron is the base metal and the primary constituent of stainless steel.
- Statement 2 is Correct: Carbon is added to the alloy (typically between 0.03% and 1.2%) to enhance hardness and tensile strength. Without carbon, the iron would be too soft for many structural applications.
- Statement 3 is Correct: Stainless steel contains Chromium (minimum 10.5%), which is essential for corrosion resistance. Nickel and Manganese are often added to improve ductility, toughness, and workability.
- Statement 4 is Incorrect: Stainless steel does not rust easily in moist air. The Chromium present in the alloy reacts with oxygen to form a thin, stable, and invisible passive layer of chromium oxide on the surface. This layer prevents further oxidation and protects the underlying metal from rusting.
Key Takeaway: Stainless steel is an alloy of Iron, Carbon, Chromium, Nickel, and Manganese. Its resistance to rusting is primarily due to the formation of a protective Chromium Oxide layer.