Among the alkali metals Li , Na , K , Rb , and Cs , the number of metals that form predominantly a superoxide upon heating in excess air AND have a density less than 1.0 g cm ⁻³ is

Step-by-step solution

Alkali metals that form predominantly superoxides when heated in excess air are K , Rb , and Cs . The densities of the given alkali metals are approximately: Li = 0.53 g cm ⁻³ Na = 0.97 g cm ⁻³ K = 0.86 g cm ⁻³ Rb = 1.53 g cm ⁻³ Cs = 1.90 g cm ⁻³ The metals with a density less than 1.0 g cm ⁻³ are Li , Na , and K . The only metal satisfying both conditions (forming a superoxide and having density Therefore, the number of such metals is 1 . Answer: 1