The correct answer is option 1: Lithium. Lithium is the least reactive with water among the given elements.

To understand why, let`s look at the reactivity of alkali metals with water. Alkali metals, such as lithium, sodium, potassium, and cesium, are highly reactive metals. When they come into contact with water, they react vigorously.

When alkali metals react with water, they undergo a displacement reaction, where the metal displaces the hydrogen in water, forming metal hydroxide and releasing hydrogen gas. The reactivity of alkali metals with water increases down the group, meaning that the reactions become more vigorous as you move from lithium to cesium.

While lithium is reactive with water, it is the least reactive among the given elements. Sodium, potassium, and cesium are more reactive than lithium, meaning they undergo more vigorous reactions with water.

Therefore, option 1: Lithium is the least reactive with water among the given elements.