Choose skeletal chemical equation from the following.

Skeletal chemical equation: The chemical equation which represents

 a true reaction the species are unbalanced in that.

Ex: ${\text{KNO}}_{\text{3}}\to {\text{KNO}}_{\text{2}}+{\text{O}}_{\text{2}}$  

${\text{H}}_{\text{2}}\text{+}{\text{O}}_{\text{2}}\to {\text{H}}_{\text{2}}\text{O}$  and $\text{Mg}+{\text{O}}_{\text{2}}\to \text{MgO}$