The density of alkali metals is in the order :

<p>Alkali metals are part of Group 1 on the periodic table and include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). As you move down the group, the atomic radius increases due to the addition of energy levels (shells). While you might think that the increased atomic mass would correspond to an increase in density, the increase in atomic radius generally outpaces the increase in atomic mass, leading to a decrease in density.</p> <p>The densities (at room temperature) of the mentioned alkali metals are :</p> <ul> <li>Sodium (Na) : 0.97 g/cm³</li> <li>Potassium (K) : 0.86 g/cm³</li> <li>Rubidium (Rb) : 1.53 g/cm³</li> <li>Cesium (Cs) : 1.93 g/cm³</li> </ul> <p>So, the order of densities is : K &lt; Na &lt; Rb &lt; Cs</p>