Which of the following elements has the greatest first ionization energy?

Answer and explanation

Correct answer: B. Helium (He)

  1. Step 1: First ionization energy increases across a period and decreases down a group. Step 2. Helium has a filled shell with maximal effective nuclear charge and minimal electron shielding. Step 3. Helium has the highest first ionization energy () of all known elements. Answer: Helium (He). Why not the others: Helium's tightly held 1s shell exceeds even fluorine and neon.

Practise more Chemistry: Stoichiometry, Equilibrium, Kinetics and Bonding.

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