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  3. Chemistry
  4. Within each pair of elements F Cl , S Se, and Li Na, respectively, the elements that release more energy upon an electron gain are :

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Q. Within each pair of elements F & Cl , S & Se, and Li & Na, respectively, the elements that release more energy upon an electron gain are :

JEE MainJEE Main 2020Classification of Elements and Periodicity in Properties

Solution:

Down the group electron affinity decrease due to increasing size. So, the electron affinity of $S > Se$ and $Li > Na$ so energy release will also be more. But in case of $F$ and $Cl$, there is exception, $Cl > F$. It is due to the small size of $F$ atom where the incoming electron face high electron-electron repulsion. So, the energy release will be more in Cl.