The compound which is not formed during the dry distillation of a mixture of calcium formate and calcium acetate is 

The following compounds are obtained when a mixture of calcium formate and calcium acetate are subjected to dry distillation : 

$$\begin{gathered} \underset{\mathrm{Calcium} \mathrm{acetate}}{{\left(\mathrm{HCOO}\right)}_2\mathrm{Ca}}\stackrel{∆}{\to }\underset{\mathrm{Methanal}}{\mathrm{HCHO}}+{\mathrm{CaCO}}_3 \\ \underset{\mathrm{Calcium} \mathrm{acetate}}{{\left({\mathrm{CH}}_3\mathrm{COO}\right)}_2\mathrm{Ca}}\stackrel{∆}{\to }\underset{\mathrm{Propanone}}{{\mathrm{CH}}_3{\mathrm{COCH}}_3}+\mathrm{CaC}{O}_3 \\ (\mathrm{HCOO}{)}_2\mathrm{Ca}+{\left({\mathrm{CH}}_3\mathrm{COO}\right)}_2\mathrm{Ca}\stackrel{\mathrm{\Delta }}{⟶}\underset{\text{ Ethanal }}{2{\mathrm{CH}}_3\mathrm{CHO}}+{\mathrm{CaCO}}_3 \end{gathered}$$

Thus, only propanal is not formed.