Step 1: Understanding the Concept:
Fuels are substances that release energy (usually heat) through a chemical reaction, typically combustion. They are classified by their physical state: solid, liquid, or gas.
Step 2: Key Formula or Approach:
Identify the physical state of each option at room temperature:
Diesel: Liquid (petroleum derivative).
Natural gas: Gas (primarily methane).
Coal: Solid (carbonaceous sedimentary rock).
Kerosene: Liquid (petroleum derivative).
Step 3: Detailed Explanation:
Coal is a fossil fuel that is mined from the earth in solid chunks. It is composed primarily of carbon, along with varying amounts of other elements like hydrogen, sulfur, oxygen, and nitrogen. It is the most widely used solid fuel for electricity generation and industrial processes like steel production.
Step 4: Final Answer:
Coal is a solid fuel.