The correct order of electron gain enthalpy is:

Electron gain enthalpy is the amount of energy released when an element accepts an electron. The process is endothermic.

correct order of electron gain enthalpy is  $\mathrm{O}<\mathrm{S}>\mathrm{Se}>\mathrm{Te}$

$\Rightarrow \mathrm{S}>\mathrm{Se}>\mathrm{Te}>\mathrm{O}$

(Oxygen shows least electron gain enthalpy due to small size of atom)