Which element has the lowest first ionization energy in Period 3?
Answer and explanation
Correct answer: A. Sodium (Na)
- Step 1: Ionization energy generally increases across a period from left to right. Step 2. Sodium is the alkali metal at the beginning of Period 3 with only one loosely held 3s electron, having the lowest first ionization energy (496 kJ/mol). Answer: Sodium (Na). Why not the others: Magnesium is higher (738 kJ/mol) with full 3s^2; Chlorine is high (1251 kJ/mol); Argon is highest in period (1521 kJ/mol).
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