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Which of the following gas gives a dense white fumes when brought near a glass rod dipped in ammonia?
1. H2
2. HCl
3. CO2
4. SO2

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Correct Answer - Option 2 : HCl


  • The gas which when brought near a glass rod dipped in ammonia gives dense white fumes is HCl.
  • The reaction that takes place is:

NH3 + HCl → NH4Cl ( dense white fumes)

  • The dense white fumes are due to the formation of gaseous Ammonium chloride NH4Cl.


  • HCl is a colorless, gas that is acidic in nature.
  • HCl turns blue litmus paper red.
  • SO2 is also an acidic gas.
  • The detection of SO2 can be done by its reaction with lime water. It turns lime water milky due to the formation of Calcium Sulphite, a white insoluble precipitate.
  • The reaction is:

Ca(OH)2 + SO2 → CaSO3

  • Similarly, CO2 also turns lime water milky.

Ca(OH)2 + CO2 → CaCO3

  • H2 burns with a pop sound.

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