a. Exothermic- potential energy in charcoal release as heat energy

b. Endothermic- Energy taken in to break the hydrogen bond of water to change from liquid to gaseous state

c. Endothermic-Energy taken in to break bond between molecules to change from solid to liquid state

To make a good explosion, the energy difference must be negative in value (exothermic)
The bigger the energy difference of the reaction, the more exothermic the reaction is. Hence to make a good explosion, relative bond strength of the product must be larger than those of the reactants which will lead to negative net energy change which is equal to a large exothermic reaction.

Heat refers to energy that flows from hotter to colder object. temperature determine the direction of heat flow.
Heat is the motion of energy and temperature is the measure of the speed of that energy.

a. Octane rating of 98 means that 98% isooctane and 2%heptane
b. No. Oxygenates are MTBE and ethanol. They have octane rating of over 100.