To determine which statement is incorrect regarding group 1A hydroxides, we will analyze each statement one by one.
### Step 1: Analyze the first statement
**Statement 1**: The dissolution of group 1A hydroxides is endothermic.
- **Analysis**: When group 1A hydroxides (like sodium hydroxide, NaOH) are dissolved in water, they release a significant amount of heat. This process is exothermic, not endothermic. Therefore, this statement is incorrect.
### Step 2: Analyze the second statement
**Statement 2**: Group 1A hydroxides are hygroscopic.
- **Analysis**: Group 1A hydroxides, such as sodium hydroxide and potassium hydroxide, can absorb moisture from the air. This property makes them hygroscopic. Therefore, this statement is correct.
### Step 3: Analyze the third statement
**Statement 3**: Group 1A hydroxides form ionic crystals.
- **Analysis**: Group 1A hydroxides are indeed ionic compounds. For example, sodium hydroxide (NaOH) consists of Na⁺ and OH⁻ ions, and they form ionic crystals. Thus, this statement is correct.
### Step 4: Analyze the fourth statement
**Statement 4**: Aqueous solutions of group 1A hydroxides are strongly basic in nature.
- **Analysis**: Aqueous solutions of group 1A hydroxides, such as NaOH, are strongly basic. They dissociate in water to produce hydroxide ions (OH⁻), which makes the solution basic. Therefore, this statement is also correct.
### Conclusion
After analyzing all four statements, we find that:
- Statement 1 is incorrect because the dissolution of group 1A hydroxides is exothermic, not endothermic.
- Statements 2, 3, and 4 are correct.
Thus, the incorrect statement is **Statement 1**.
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