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Q36 (NDA-I/2008) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

When iron is left exposed in open air, it gets rested. Which costituent (s) of air is/ are responsible for rusting iron? 1. Oxygen gas present in air 2. Moisture present in air 3. Carbon dioxide gas present in air Select the correct answer using the code given below :

Result
Your answer: —  Â·  Correct: C
Explanation

Rusting is a specific form of corrosion that occurs when iron is exposed to both oxygen and moisture (water) for a prolonged period [2]. Chemically, it is an oxidation-reduction reaction where iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide, commonly known as rust [3]. While carbon dioxide is a constituent of air and can react with other metals like copper to form basic copper carbonate, it is not a primary requirement for the rusting of iron [4]. Experimental evidence shows that iron does not rust in dry air (lacking moisture) or in air-free water (lacking oxygen). Therefore, only oxygen and moisture are the essential constituents of air responsible for the formation of rust on iron surfaces [2].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.5 CORROSION > p. 53
  2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 4: The World of Metals and Non-metals > Activity 4.5: Let us experiment > p. 50
  3. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.3.1 Rusting > p. 62
  4. [4] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > 1.3.1 Corrosion > p. 13
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