Concept:Chemical energy stored in a fuel is directly converted into heat energy through a combustion reaction, without any intermediate form of energy.
Explanation:Burning wood is the best example because wood contains chemical energy in the form of cellulose and lignin.
During combustion, wood reacts with oxygen from the air in an exothermic reaction.
This reaction breaks the chemical bonds in wood and forms new bonds, releasing a large amount of heat energy directly.
The combustion reaction can be represented as:
Wood+O2​→CO2​+H2​O+heat.
In the other options, the conversion is indirect or involves different energy forms.
A battery lighting a bulb first converts chemical energy to electrical energy, then to light and heat.
A motor running on electricity converts electrical energy to mechanical energy, not chemical to heat.
A solar cooker converts light energy (solar) to heat energy, with no chemical energy involved.
Thus, only burning wood directly transforms chemical energy into heat energy without any intermediate step.
Answer:D. Burning of wood