The most vigorous reaction when dropped in water has K.
Potassium (K) is higher in activity series of metals than other metals in this question.
Activity series is an empirical progression of a series of metals, arranged by their reactivity from highest to lowest (alkaline metals have highest reactivity and Noble metals lowest reactivity).
Potassium (K) is a chemical element with atomic number 19 (number of electrons is 19).
Electron configuration of potassium is: ₁₉K 1s²2s²2p⁶3s²3p⁶4s¹.
Potassium is the alkali metal and has a single valence electron in the outer electron shell.
All alkaline metals (I group of periodic table, Na, K, Cs...) loose one electron in chemical reaction and react vigorously with water.
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