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MHT CET Medical202623 April 2026Evening ShiftChemistryThermodynamics (C)Actual

Which of the following physical transformations is an exothermic?

Options

  1. AEnthalpy of ionisation of one mole of gaseous sodium atom.
  2. BElectron gain enthalpy of one mole of gas phase atoms of chlorine.
  3. CEnthalpy of atomization of one mole of methane gas.
  4. DEnthalpy of solution of one mole of sodium chloride in specified amount of water.

Correct answer

B. Electron gain enthalpy of one mole of gas phase atoms of chlorine.

Step-by-step solution

Enthalpy of ionisation of one mole of gaseous sodium atom is the energy required to remove an electron from an isolated gaseous atom, which is always an endothermic process ( H > 0 ). Electron gain enthalpy of one mole of gas phase atoms of chlorine is the energy released when an electron is added to an isolated gaseous chlorine atom. Halogens have highly negative electron gain enthalpies, making this process exothermic ( H Enthalpy of atomization of one mole of methane gas involves breaking all the C-H bonds to fo

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