Concept:Different alkali metals exhibit very specific, characteristic behaviors when reacting with water, primarily distinguished by reaction vigor and flame color.
Solution:- Lithium: Reacts steadily, floats, but does not usually melt into a ball or catch fire. (Flame: Crimson).
- Sodium: Reacts vigorously with cold water. The reaction is so exothermic that it melts the Sodium into a silver ball that darts across the water's surface. If it ignites, it burns with a characteristic yellowish-golden flame.
- Potassium: Reacts explosively, instantly catching fire with a lilac/violet flame.
- Based on the exact visual descriptors (melts into a ball, vigorous but not instantly explosive, golden-yellow flame), the metal is definitively Sodium.
Why other options are incorrect:- The flame colors and reaction speeds rule out Li (crimson, slower), K (lilac, explosive), and Ca (sinks, brick-red flame).
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