When an alkali metal reacts with water, the most common gas that is produced is hydrogen (option 1). Alkali metals are highly reactive and have only one electron in their outermost shell. When they come into contact with water, they readily donate this electron to form a positive ion. In the process, hydrogen gas is released.
Option 2 (oxygen) is incorrect because oxygen gas is not produced when alkali metals react with water. Oxygen is already present in water as the oxygen atom forms a part of the water molecule, but it is not released as a gas during the reaction.
Option 3 (hydrogen peroxide) is also incorrect. Hydrogen peroxide is not produced when alkali metals react with water. Hydrogen peroxide is a compound composed of hydrogen and oxygen, but it is not formed in the reaction between alkali metals and water.
Option 4 (ozone) is incorrect as well. Ozone is an allotrope of oxygen and is not produced when alkali metals react with water.
Therefore, the correct answer is hydrogen gas (option 1).