Which one of the alkali metals forms only the normal oxide, `M_(2)O`, on heating in air ?

Options

A. `Li`
B. `Na`
C. `Rb`
D. `K`

Answer

A

Explanation

`Li^(+)` being smallest possessses strong positive field and, thus, combines with small anion `O^(2-)` to form stable `Li_(2)O` compound. The `Na^(+),K^(+)` and `Rb^(+)` being relatively larger exert less strong positive field around them and thus react with larger oxygen anions, `i.e., O_(2)^(2-)` and `O_(2)^(1-)` to form stable oxides.