Which element has the highest first ionisation energy?
Answer and explanation
Correct answer: A. Helium
- Step 1: First ionization energy represents the energy required to remove the outermost valence electron from an isolated gaseous atom.
- Step 2: Helium has a stable closed-shell duplet configuration with minimal atomic radius and maximum effective nuclear charge attraction without inner-shell shielding.
- Step 3: Consequently, Helium exhibits the highest first ionization energy among all chemical elements.
Answer
Helium.
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