The element with positive electron gain enthalpy value is

$\text{F}(Z=9)\to \text{\hspace{0.17em}VIIA\hspace{0.17em}group,\hspace{0.17em}2nd period}$; $\text{C}l(Z=17)\to \text{\hspace{0.17em}VIIA\hspace{0.17em}group\hspace{0.17em}\&\hspace{0.17em}3rd\hspace{0.17em}period}$

$\text{He}(Z=4)\to \text{VIII\hspace{0.17em}group}$; $\text{Cs}(Z=55)\to \text{\hspace{0.17em}IA\hspace{0.17em}group,\hspace{0.17em}Alkali\hspace{0.17em}metal}$

Note: For inert gases or VIIIA group elements E.A is positive.

IA group elements have least E.A values but VIIA group elements have positive E.A values. As fluorine is 2^nd period element it has small E.A value than Cl.