The correct option for the question is **A. Z is efflorescent**. ### Explanation of the Correct Answer 1. **Understanding Efflorescence**: - Efflorescent substances are those that lose water of crystallization when exposed to air. This process can lead to the formation of a dry powdery substance. When salt Z became liquid, it indicates that it had lost its water of crystallization and possibly absorbed moisture from the air, leading to a liquid state. 2. **Analyzing Salt Y**: - Salt Y gained weight overnight. This suggests that it absorbed moisture from the air. This behavior is characteristic of hygroscopic substances, which can attract and hold water vapor from the environment. 3. **Conclusion**: - Since Z became liquid, it is likely that it is efflorescent, as it lost water and possibly formed a solution. Y, on the other hand, gained weight, indicating it is hygroscopic. Therefore, the conclusion is that Z is efflorescent. ### Why the Other Options are Incorrect - **Option B: Y and Z are efflorescent**: - This option is incorrect because if both salts were efflorescent, Y would have lost weight (due to loss of water), not gained weight. Therefore, this option contradicts the observed behavior of Y. - **Option C: Y and Z are deliquescent**: - Deliquescent substances absorb moisture from the air to the extent that they dissolve in the absorbed water, forming a liquid solution. While Z becoming liquid might suggest deliquescence, Y gaining weight does not support this. If Y were deliquescent, it would also have dissolved and not just gained weight. - **Option D: Y and Z are hygroscopic**: - While Y is hygroscopic (as it gained weight), Z cannot be classified as hygroscopic because it became liquid. If Z were hygroscopic, it would have absorbed moisture but would not have transitioned to a liquid state. Therefore, this option is misleading. ### Summary of Key Concepts - **Efflorescent Salts**: Lose water of crystallization and may form a dry powder. - **Hygroscopic Salts**: Absorb moisture from the air, leading to an increase in weight. - **Deliquescent Salts**: Absorb enough moisture to dissolve in the water they attract, forming a liquid solution. - **Observation Analysis**: Always analyze the behavior of substances in relation to their interaction with moisture to draw conclusions about their properties. ### Revision Summary - **Efflorescent**: Salts that lose water and may become dry. - **Hygroscopic**: Salts that gain moisture from the air. - **Deliquescent**: Salts that absorb moisture and dissolve in it. - **Observation**: Analyze changes in weight and state to determine the nature of salts.