UPSC CAPF (AC) 2025 Paper I · Question 100
Question 100 of the UPSC CAPF (AC) 2025 Paper I (3 August 2025). Try it first, then open the answer and explanation.
Which one of the following is not an exothermic reaction?
- Dissolution of calcium oxide in water
- Decomposition of vegetable matter into compost
- Decomposition of lead nitrate
- Dilution of sodium hydroxide with water
निम्नलिखित में से कौन-सी ऊष्माक्षेपी अभिक्रिया नहीं है?
- कैल्सियम ऑक्साइड का जल में विलयन
- वनस्पति पदार्थ का खाद में अपघटन
- लेड नाइट्रेट का अपघटन
- सोडियम हाइड्रॉक्साइड का जल से तनुकरण
Show answer
Answer: (3) Decomposition of lead nitrate
उत्तर: (3) लेड नाइट्रेट का अपघटन
Lead nitrate decomposes only on continued heating (2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂); like other thermal decomposition reactions it absorbs heat, i.e. it is endothermic. Calcium oxide reacting with water (slaking of lime), the decomposition of vegetable matter into compost and the dilution of sodium hydroxide all release heat, i.e. they are exothermic.