Question

B. ne chemical reaction involved in burning wood

Answer 1

B. a combustion reaction involves a hydrocarbon burning with oxygen gas to produce water and carbon dioxide.
C. this is an endothermic reaction since ΔH would be positive.
3.  I am pretty sure it is referring to the activation energy which is a characteristic all chemical reaction have and in a combustion reaction the spark gets the reaction over the activation energy.
4.  K₂O(s)+CO₂(g)⇒K₂CO₃(s)+energy
The energy level of the reactants is higher than the energy level of the products (you can see this with energy diagrams).

5. 2HgO(s)+energy⇒2Hg(l)+O₂(g)
the energy levels of the products is higher than the energy level of the reactants. (this can also be seen with energy diagrams)