Question

Which of the following elements would have the lowest first ionization energy?

• A. Fluorine
• B. Oxygen
• C. Nitrogen
• D. Carbon
• E. Boron

Answer 1

The correct option is E Boron

Boron, carbon, nitrogen, oxygen, fluorine have respectively 3, 4, 5, 6, 7 electrons in their outermost orbit. Along a period, as the number of valence electrons increases, the nuclear charge of the atom increases and so the nuclear force of attraction on these valence electrons also increases. Thus, the nuclear force of attraction on the 7 valence electrons of fluorine will be the highest. And the nuclear force of attraction on the 3 valence electrons of boron will be the lowest.

Since the nuclear charge and nuclear force of attraction in case of boron is the lowest, it is easy to remove boron's valence electrons. Thus, boron will have the lowest first ionization energy.

Option E is the correct answer.