How do hygroscopic and deliquescent substances differ? Give examples, and explain why common salt becomes wet in the rainy season.

1. 1 · Define hygroscopic. A hygroscopic substance absorbs moisture from the air but does not dissolve in it, so its state does not change.
2. 2 · Define deliquescent. A deliquescent substance absorbs so much moisture from the air that it dissolves and forms a solution.
3. 3 · Draw a comparison table. [Two columns, hygroscopic and deliquescent: what happens, change of state, two examples each]
4. 4 · Examples.
   • Hygroscopic: conc. H₂SO₄, quicklime, silica gel
   • Deliquescent: CaCl₂, MgCl₂, NaOH
5. 5 · Common salt in the rainy season. Its MgCl₂ and CaCl₂ impurities are deliquescent, so they absorb moisture and dissolve, making the salt damp.
6. 6 · Real-life link. Silica gel sachets keep medicines and shoes dry because silica gel is hygroscopic.
7. 7 · Close in one line. Thus both absorb moisture, but only deliquescent substances dissolve in it.

Scoring tip: The key difference is whether the substance dissolves. Name the impurities MgCl₂ and CaCl₂ for the salt question.