Which of the following forms the connecting link between glycolysis and Kreb's cycle

Write down the names of missing intermediate compounds in a sequence in the given diagrammatic representation of Kreb’s cycle.

In the following reaction, identify $\mathrm{X}$ and $\mathrm{Y}$ respectively: 

$\mathrm{Pyruvic} \mathrm{acid}+\mathrm{CoA}+{\mathrm{NAD}}^{+}\underset{\mathrm{x}}{\overset{{\mathrm{Mg}}^{2+}}{\to }}\mathrm{Y}+{\mathrm{CO}}_2+\mathrm{NADH}+{\mathrm{H}}^{+}$

Match the metabolic pathways in Column I with their corresponding intermediate molecules listed in Column II

Choose the CORRECT combination.

Identify the reactions where energy is produced:

I. $\mathrm{Malic} \mathrm{acid}+{\mathrm{NAD}}^{+} \stackrel{\mathrm{Malate}dehydrogenase}{⟶} \mathrm{oxaloacetic} \mathrm{acid}+\mathrm{NADH}$

II. $\mathrm{Citric} \mathrm{acid} \stackrel{\mathrm{Aconitase}}{⟶} \mathrm{cis}-\mathrm{aconitic} \mathrm{acid}+{\mathrm{H}}_2\mathrm{O}$

III. $\mathrm{Succinic} \mathrm{acid}+\mathrm{FAD} \stackrel{ \mathrm{Succinic} \mathrm{dehydrogenase} }{⟶} \mathrm{Fumaric} \mathrm{acid}+{\mathrm{FADH}}_2$

IV.  $\mathrm{Succinyl} \mathrm{CoA}+\mathrm{ADP}+\mathrm{Pi} \underset{\mathrm{Thiokinase}}{\overset{\mathrm{Succinic}}{\to }} \mathrm{Succinic} \mathrm{acid}+\mathrm{ATP}+\mathrm{CoA}$

V. $\mathrm{Oxalosuccinic} acid\underset{ \mathrm{decarboxylase}}{\overset{\mathrm{Oxalosuccinic} }{\to }} \mathrm{\alpha }-\mathrm{Ketoglutaric} \mathrm{acid}+{\mathrm{CO}}_2$

The correct combination is: