Which metal reacts most vigorously with water?
(A) Ca (B) K (C) Mg (D) Na
The given answer is B and the reasoning is that is is the most electropositive since it the furthest left and down according to periodic trends.
However, isn't $\ce{K}$ the conjugate acid from a strong base -- $\ce{KOH}$? So isn't the conjugate base of a strong acid quite weak? So why would $\ce{K}$ react strongly?
Answer
I might be wrong here, but I believe that the question asks about the metals in their atomic (non ionic) form.
In order for a $\ce{KOH}$ bond to form, the K must be ionized (since the $\ce{KOH}$ bond is ionic). This means that when $\ce{KOH}$ dissolves in water it'll form the $\ce{K}^+$ electrolyte, which is not the same thing as a pure $\ce{K}$ atom with its 19th electron.
A $\ce{K}$ atom, then, since it's the most electropositive of that list, is the one to react "more vigorously" (which I guess it refers to more speed/energy) with water (a polar molecule).
I hope this helped you. I'm sorry if I'm wrong!
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