Correct Option
The correct option isCoal is primarily composed of carbon which reacts with atmospheric oxygen.
Explanation
Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. Coal is a fossil fuel primarily composed of carbon. When heated in the presence of air, the carbon constitutes the fuel that undergoes oxidation.
Option Analysis
- Coal contains oxygen which reacts internally with carbon. is incorrect: While coal contains trace amounts of oxygen, nitrogen, and sulfur, the primary source of oxygen for combustion is the atmosphere, not the internal composition of the coal itself.
- Coal is primarily composed of carbon which reacts with atmospheric oxygen. is correct: Coal is an allotrope of carbon (amorphous). When heated, the carbon atoms gain sufficient energy to react with atmospheric oxygen ($O_2$). This chemical reaction results in the formation of carbon dioxide ($CO_2$) and the release of energy. The chemical equation is:
$C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)} + Heat$ - Heating releases carbon dioxide trapped within the coal matrix. is incorrect: Carbon dioxide is not pre-existing or "trapped" inside the coal matrix in significant quantities. It is generated as a new product through the chemical reaction between carbon and oxygen.
- Coal undergoes thermal decomposition into water and gas. is incorrect: Thermal decomposition refers to the breakdown of a substance by heat in the absence of oxygen (pyrolysis). While heating coal without air produces coke, coal tar, and coal gas, heating it in air leads to combustion (oxidation), producing carbon dioxide.
Key Takeaway: The production of carbon dioxide from coal is an oxidation reaction where the carbon content of the fuel reacts chemically with atmospheric oxygen.