The density of alkali metals is in the order (A) Na < Rb < K < Cs (B) K<Na < Rb < Cs (C) K<Cs <Na < — JEE Mains Chemistry Past Papers Chemistry Question

💡 Solution & Explanation

Density increase down the group but K is lighter than Na. Order = Li < K < Na < Rb < Cs Density / g cm–3 ; Li = 0.53 ; Na = 0.97 ; K = 0.86 ; Rb = 1.53 ; Cs = 1.90 Due to their large size the atoms of alkali metals are less closely pocked. Consequently have low density On going down the group, both the atomic size and atomic mass increase but the increase in atomic mass compensates the bigger atomic size. As a result, the density of alkali metals increases from Li to Cs. K is however, lighter then Na. It is probably due to an unusual increase in atomic size of potassium.