Question

Consider the following reaction:
$M+O_2\to M{O}_2$
$M$ is an alkali metal$M{O}_2$ is a stable superoxide

• A. $M$ can not be $Li$ and $Na$
• B. $M$ can not be $Cs$ and $Rb$
• C. $M$ can not be $Li$ and $Rb$
• D. None of these

Answer 1

The correct option is A $M$ can not be $Li$ and $Na$

Lithium only forms monoxide when heated in oxygen. Sodium forms monoxide and peroxide in excess of oxygen.
They do not form stable superoxide.
Thus, M can not be Li and Na.