Chromium, calcium, and potassium are near each other on the periodic table and have some common characteristics but differ in chemical reactivity. Which lists these metals in order from most reactive to least reactive?

Potassium is the most reactive of these metals, followed by calcium, then chromium. Potassium reacts vigorously because it readily loses its single outer electron; calcium is also reactive but loses electrons less readily. Chromium is a transition metal and is least reactive of the three. Therefore, the order is potassium, calcium, chromium, choice C.

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