The Group 1 elements in the periodic table are known as the alkali metals. They include lithium, sodium and potassium, which all react vigorously with water to produce an alkaline solution (a basic solution)
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They must be stored under oil to keep air and water away from them.
All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group, as the atoms attract the electron less strongly, so less potential energy needs to be spent, and more is available for kinetic energy
More details: http://www.chemguide.co.uk/inorganic/group1/reacth2o.html