Select the incorrect statement(s):

Options

A. KOH is a weaker base than NaOH
B. Milk of magnesia is an aqueous solution of `Mg(OH)_(2)`
C. `Mg^(2+)` ions are precipitated with the addition of `NH_(4)OH` in the presence of `NH_(4)Cl`
D. `CaO_(2)` is less stable than `MgO_(2)`

Answer

To solve the question of selecting the incorrect statements regarding s-block elements, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: KOH is a weaker base than NaOH.**
- **Analysis:** The basicity of hydroxides increases as we move down the group in the periodic table. This is due to the decrease in ionization enthalpy, which allows for easier release of hydroxide ions (OH⁻). Since potassium (K) is below sodium (Na) in Group 1, KOH is actually a stronger base than NaOH.
- **Conclusion:** This statement is **incorrect**.

2. **Statement 2: Milk of Magnesia is an aqueous solution of Mg(OH)₂.**
- **Analysis:** Milk of Magnesia is indeed an aqueous suspension of magnesium hydroxide (Mg(OH)₂), which is formed when magnesium ions (Mg²⁺) react with hydroxide ions (OH⁻).
- **Conclusion:** This statement is **correct**.

3. **Statement 3: Mg²⁺ ions are precipitated with the addition of NH₄OH in the presence of NH₄Cl.**
- **Analysis:** The presence of NH₄Cl introduces NH₄⁺ ions, which suppress the ionization of NH₄OH due to the common ion effect. This results in a lower concentration of OH⁻ ions, which is not sufficient to exceed the solubility product of Mg(OH)₂. Therefore, Mg²⁺ ions do not precipitate.
- **Conclusion:** This statement is **incorrect**.

4. **Statement 4: CaO₂ is less stable than MgO₂.**
- **Analysis:** The stability of peroxides in Group 2 increases as we move down the group due to the larger ionic radius of the cations. Therefore, CaO₂ should be more stable than MgO₂, not less.
- **Conclusion:** This statement is **incorrect**.

### Final Answer:
The incorrect statements are:
- Statement 1: KOH is a weaker base than NaOH.
- Statement 3: Mg²⁺ ions are precipitated with the addition of NH₄OH in the presence of NH₄Cl.
- Statement 4: CaO₂ is less stable than MgO₂.