The answer is - a. Alkali Metal. They react violently with water to form alkaline solutions. This is because they all have 1 electron in their outer shell and losing 1 electron allows them to have full outer shells, and achieve stability.
The most vigorous reaction with water is shown by alkali metals, particularly sodium and cesium. They react with water to produce hydrogen gas and a metal hydroxide. Therefore, the correct option is A. Alkali metal.
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