Question

Arrange Li, Na, K, Rb, Cs in order of increasing ionization energy:

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

Answer 1

Answer: (A)

$Cs<Rb<K<Na<Li$

Concept: As we move from top to bottom in group the ionization energy will be decreased,because the atomic radius will be increased so the removal electron will be easy.
Li, Na, K, Rb, Cs are IA group elements from Li to Rb the ionization energy
will be decreased. So, the correct order of ionization energy is $Cs<Rb<K<Na<Li$
Hence, option A is correct.