Question

Why do lithium, sodium and potassium float on water?

Answer 1

If and only if the density of water is greater than the density of the substance or element, it will float on water. The element will experience buoyancy when floating on the water's surface. Metals with a denser density than water will sink.

Complete answer:
Lithium, sodium, and potassium are all very light elements, and metals which are made purely of them will have low densities
When alkali metals are added to water, they produce a significant amount of heat. Because of the huge quantity of energy released when it combines with water. As a result, the reaction between alkali metals and water is exothermic.
The rate of metals reacting with water increases significantly as we move down the alkali metals group. This is due to an increase in the energy of hydration. As a result, the reaction becomes more exothermic. However, when we use alloy, it occasionally floats on the water's surface. The metal potassium is the most reactive.

Note:
Alkali elements have the lowest density due to their large radius and volume. As a result, they are extremely soft and easily cut with a knife. Water is heavier than lithium, sodium, and potassium. Among the alkali metals, potassium has the lowest density. Alkali metals have low melting and boiling temperatures compared to other period elements due to their soft nature. From Lithium to Caesium, the melting and boiling points decrease.