To solve the question regarding substances X, Y, and Z, we need to analyze the information provided about each substance and determine which statement is incorrect.
### Step-by-Step Solution:
1. **Identify Substance X**:
- X is described as a gaseous fuel obtained by the strong heating of coal in the absence of air.
- This process is known as destructive distillation of coal, which produces gases like methane, hydrogen, and carbon monoxide.
- Therefore, X can be identified as **coal gas**.
2. **Identify Substance Y**:
- Y is described as a thick black liquid with an unpleasant smell, obtained by heating coal in the absence of air.
- This substance is known as **coal tar**, which is a complex mixture of various organic compounds.
- It can be separated into different substances through processes like distillation.
3. **Identify Substance Z**:
- Z is described as a tough and porous black solid prepared by heating coal in the absence of air.
- This substance is known as **coke**, which is primarily composed of carbon and is used in metallurgy, especially in the production of iron.
4. **Evaluate Statements**:
- Now that we have identified X, Y, and Z, we can evaluate the statements about them.
- X is a gaseous fuel (coal gas).
- Y is a thick black liquid (coal tar).
- Z is a tough black solid (coke).
- We need to find the statement that is incorrect about these substances.
5. **Determine the Incorrect Statement**:
- If a statement claims that X, Y, or Z has properties that do not align with their definitions (e.g., calling coke a liquid), that would be the incorrect statement.
- Based on the information provided, if any statement incorrectly describes the properties or composition of these substances, that would be the answer.
### Conclusion:
After analyzing the properties of substances X, Y, and Z, we conclude that the incorrect statement is likely one that mischaracterizes one of these substances.
