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Which of the following sequences lists the given metals in decreasing order of their standard electrode potentials: Mg, K, Ba and Ca?

1. K, Ca, Ba, Mg
2. Ba, Ca, K, Mg
3. Ca, Mg, K, Ba
4. Mg, Ca, Ba, K

Correct answer: K, Ca, Ba, Mg

Solution

Standard reduction potentials for these metals are approximately K < Ca < Ba < Mg in increasing negativity, so in decreasing order of E° they are K, Ca, Ba, Mg. This matches the sequence from highest to lowest electrode potential.

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