Step 1: Understanding the Concept:
Water gas is an important industrial synthesis gas used for producing methanol and other hydrocarbons. It is a combustible gas mixture.
It is produced through the gasification of coal or coke. When steam is passed over incandescent (red-hot) coke at high temperatures (around 1270 K), a redox reaction occurs.
Step 2: Key Formula or Approach:
The reaction for the formation of water gas is:
\[ C(s) + H_2O(g) \xrightarrow{1270 K} CO(g) + H_2(g) \]
Since the mixture consists of carbon monoxide and hydrogen, it is referred to as "water gas" because the hydrogen comes from the water (steam) molecules.
Step 3: Detailed Explanation:
- Option (1): \( CO + H_2 \). This is the correct chemical composition of water gas. It is also sometimes called "synthesis gas" or "syngas" because of its role in synthetic chemical manufacturing.
- Option (2): \( CO_2 + H_2 \). This mixture is produced in the water-gas shift reaction, but it is not called water gas.
- Option (3): \( H_2O + CH_4 \). These are the reactants used in the "steam reforming of methane" to produce syngas, not the product mixture itself.
- Option (4): \( H_2 + O_2 \). This is an explosive mixture used in fuel cells or rocket propellants, unrelated to water gas.
Step 4: Final Answer:
Water gas is composed of Carbon Monoxide (\( CO \)) and Hydrogen (\( H_2 \)).
The correct answer is therefore option (A).