In which one of the following situations a chemical reaction does not occur?

A chemical reaction involves the formation of new substances with different chemical properties. Coal burning in air is a combustion reaction where carbon combines with oxygen to form carbon dioxide [t1, t3]. Sodium reacts violently with water to produce sodium hydroxide and hydrogen gas [c2, c3]. Iron kept in moist air undergoes a chemical reaction called rusting, forming iron oxide [c1, t6]. In contrast, common salt (sodium chloride) is a highly stable ionic compound [t4, t10]. When exposed to air, it does not undergo a chemical reaction; it may only exhibit physical changes like deliquescence (absorbing moisture) if impurities like magnesium chloride are present, but the NaCl itself remains chemically unchanged. Therefore, no chemical reaction occurs when common salt is exposed to air.

Sources

1. [1] https://nitsri.ac.in/Department/Chemical+Engineering/EE1.pdf
2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 4: The World of Metals and Non-metals > Activity 4.6: Let us investigate (demonstration activity) > p. 52
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.10 > p. 43
4. [4] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Snapshots > p. 131
5. [5] https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-Chloride