Question

Consider the following reaction, $2M+\frac{1}{2}{O}_2\to M_{2}O$ ($M$ $=$ alkali metal). Select the correct statement.

• A. $M$ can be $Li$ and $Na$
• B. $M$ can be $Cs$ and $Rb$
• C. $M$ can be $Li$ and $Rb$
• D. None of the above

Answer 1

The correct option is A $M$ can be $Li$ and $Na$

On reaction with oxygen, lithium forms monoxide (${Li}_{2}O$).

$4Li\left(s\right)+O_2\left(g\right)\to 2L{i}_{2}O\left(s\right)$

and sodium,

$4Na\left(s\right)+O_2\left(g\right)\to 2N{a}_{2}O\left(s\right)$

The other alkali metals $(K,Rb,Cs,Fr)$ form superoxide compounds (in which oxygen takes the form $O^{2-}$) as the principal combustion products. The following equation shows the formation of superoxide, where $M$ represents $K,Rb,Cs,$ or $Fr$

$M\left(s\right)+O_2\left(g\right)\to M{O}_2\left(s\right)$