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The first ionization enthalpy (ΔH₁), second ionization enthalpy (ΔH₂), and electron gain enthalpy (ΔegH), all in kJ mol⁻¹, for five elements I, II, III, IV and V are listed below: Element ΔH₁ ΔH₂ ΔegH I 520 7300 -60 II 419 3051 -48 III 1681 3374 -328 IV 1008 1846 -295 V 2372 5251 +48 From these, identify the most reactive metal and the least reactive non-metal, respectively.

1. I and V
2. V and II
3. II and V
4. IV and V

Correct answer: II and V

Solution

Element II has a relatively low first ionization enthalpy, indicating it can easily lose an electron, making it the most reactive metal. Element V has a positive electron gain enthalpy, suggesting it does not favorably gain electrons, which characterizes it as the least reactive non-metal.

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