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Q63 (CDS-I/2009) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one of the following when dissolved in H2O gives hissing sound

Result
Your answer: —  Â·  Correct: D
Explanation

When water is added to quicklime (calcium oxide, CaO), a vigorous chemical reaction occurs, producing slaked lime (calcium hydroxide, Ca(OH)2) [c1, c3]. This process, known as the slaking of lime, is highly exothermic, meaning it releases a significant amount of heat energy [t4, t5]. The intense heat generated during this rapid hydration causes some of the water to instantly turn into steam, which escapes the mixture and produces a characteristic hissing sound [t3, t4]. This reaction is a classic example of a combination reaction where two reactants form a single product while evolving heat [c1, c4]. In contrast, limestone (calcium carbonate) is relatively insoluble and does not react vigorously with water, while slaked lime is the already-hydrated product of this reaction [t1, t5].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Figure 1.3 > p. 6
  2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Activity 8.1: Let us experiment > p. 118
  3. [3] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > QUESTIONS > p. 7
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SIMILAR QUESTIONS

CDS-I · 2023 · Q52 Relevance score: -3.71

Which of the following statements with regard to the reaction given below are correct? CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat 1. Quicklime is used for white-washing of walls. 2. The solution of slaked lime is used for whitewashing of walls. 3. CaO reacts slowly with CO2 in air to form a thin layer of CaCO3 on walls. 4. Calcium hydroxide called 'slaked lime' is an inorganic compound. Select the correct answer using the code given below.

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If a limestone piece is dipped in water, a bubble evolves. The bubbling is due to

NDA-II · 2019 · Q52 Relevance score: -5.00

Which one of the following does not represent the salt, Calcium carbonate?

NDA-II · 2025 · Q96 Relevance score: -5.30

The reaction that occurs on passing carbon dioxide gas through lime water is