Question

Arrange Li, Na, K, Rb, Cs in order of increasing electron-affinity:

• A. $Cs<Rb<K<Na<Li$
• B. $K<Na<Cs<Rb<Li$
• C. $Cs<K<Rb<Li<Na$
• D. None of these

Answer 1

Answer: (A)

$Cs<Rb<K<Na<Li$

Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion.
As we move from top to bottom in group the electron-affinity will be decreased, because the atomic radius will be increased so distance from outer electrons to the nucleus will be increased,so the electrons will be difficultly added Li, Na, K, Rb, Cs are IA group elements from Li to Rb the electronegativity will be decreased.so the correct order of electronegativity is $Cs<Rb<K<Na<Li$.