Here's why:

* Softness: Cesium is so soft that it can be cut with a knife at room temperature.

* Reactivity: Cesium is the most electropositive element, meaning it readily loses electrons to form positive ions. This makes it extremely reactive, especially with water. It reacts violently with water, even explosively, producing hydrogen gas and heat.

Important Note: Due to its extreme reactivity, cesium is not found in its elemental form in nature. It is a highly dangerous element and should only be handled by trained professionals in controlled environments.