What is the predicted order of first ionization energies from highest to lowest for lithium ( Li ), sodium ( Na ), potassium ( cap k ), and rubidium ( Rb )?
Answer
A
Li is greater than Na comma Na is greater than cap k comma cap k is greater than Rb
B
Rb is greater than cap k comma cap k is greater than Na comma Na is greater than Li
C
Rb is greater than cap k comma cap k is greater than Li comma Li is greater than Na
D
cap k is greater than Rb comma Rb is greater than Na comma Na is greater than Li
Explanation
These elements are all in Group 1 of the periodic table. First ionization energy generally decreases down a group because the outer electron is farther from the nucleus and more shielded, so it takes less energy to remove. From highest to lowest, the order is Li > Na > K > Rb, which matches choice B.
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