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NDA 2 2025 GAT, question 108

Topic: Chemistry

Q108

Which one of the following is an endothermic reaction ?

  1. (a) CH4 (g)+2O2 (g)→CO2 (g)+2O2 (g)CH_{4}\,(g)+2O_{2}\,(g)\to CO_{2}\,(g)+2O_{2}\,(g)
  2. (b) C6H12O6 (aq)+6O2 (g)→6CO2 (g)+6H2O (l)C_{6}H_{12}O_{6}\,(aq)+6O_{2}\,(g)\to 6CO_{2}\,(g)+6H_{2}O\,(l)
  3. (c) N2 (g)+3H2 (g)→2NH3 (g)N_{2}\,(g)+3H_{2}\,(g)\to 2NH_{3}\,(g)
  4. (d) 2Pb(NO3)2 (s)→2PbO (s)+4NO2 (g)+O2 (g)2Pb(NO_{3})_{2}\,(s)\to 2PbO\,(s)+4NO_{2}\,(g)+O_{2}\,(g)Correct answer

Solution.

Answer: (d) 2Pb(NO3)2 (s)→2PbO (s)+4NO2 (g)+O2 (g)2Pb(NO_{3})_{2}\,(s)\to 2PbO\,(s)+4NO_{2}\,(g)+O_{2}\,(g)

  1. Lead nitrate breaks down only when heated, so its decomposition absorbs heat: endothermic.
  2. Burning methane, oxidising glucose and forming ammonia all release heat.

Trap: Option (a) is misprinted (its products should include 2H2O2H_{2}O, not 2O22O_{2}), but it is methane combustion, which releases heat either way.