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JEE Main levelSingle correct optionDifficulty 2 of 3ph187

The electron gain enthalpy of F is less negative than that of Cl mainly because

  1. AF has a lower nuclear charge than Cl
  2. BF has vacant d orbitals that destabilise the added electron
  3. Cthe first ionisation enthalpy of F is lower than that of Cl
  4. Dthe very small 2p subshell of F causes strong repulsion between the added electron and the electrons already present

Answer: D

In F the added electron goes into a compact n = 2 shell where electron-electron repulsion is large, which offsets part of the energy released. Cl has the larger 3p subshell with less repulsion, so its value () is more negative than that of F (). F has the higher nuclear charge and no d orbitals in its valence shell.
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