Question
The main oxides formed on combustion of $$Li,Na$$ and $$K$$ in excess of air are, respectively :
A.
$$L{i_2}{O_2},\,N{a_2}{O_2}\,{\text{and}}\,K{O_2}$$
B.
$$L{i_2}O,N{a_2}{O_2}\,{\text{and}}\,K{O_2}$$
C.
$$L{i_2}O,\,N{a_2}O\,\,{\text{and}}\,K{O_2}$$
D.
$$Li{O_2},N{a_2}{O_2}\,{\text{and}}\,{K_2}O$$
Answer :
$$L{i_2}O,N{a_2}{O_2}\,{\text{and}}\,K{O_2}$$
Solution :
On heating with excess of air $$Li,Na$$ and $$K$$ forms following oxides
\[\begin{align}
& 4Li+{{O}_{2}}\to \underset{\text{Lithium monoxide}}{\mathop{2L{{i}_{2}}O}}\, \\
& 4Na+{{O}_{2}}\xrightarrow{575K}\underset{\text{Sodium peroxide}}{\mathop{N{{a}_{2}}{{O}_{2}}}}\, \\
& K+{{O}_{2}}\to \underset{\text{Potassium superoxide}}{\mathop{K{{O}_{2}}}}\, \\
\end{align}\]