The correct order of electron gain enthalpy is:

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Strategy:
 In Group 16, Electron Gain Enthalpy anomaly occurs at the top. Oxygen's small size leads to excessive inter-electronic repulsion, making it the least exothermic (least negative).

Step 1: Compare Group 16 elements
Magnitude trend (Descending): .
Oxygen is at the bottom of the list for magnitude because the repulsive forces in its compact  subshell dominate over the nuclear pull. Sulfur, having more space in its  subshell, has the most negative value.

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