Which of the following compounds are not base when dissolved?'

Options

A. `K_(2)O`
B. `Na_(2)O_(2)`
C. `NO_(2)`
D. `CI_(2)O_(7)`

Answer

To determine which of the given compounds are not bases when dissolved in water, we will analyze each compound one by one.

### Step 1: Analyze K2O (Potassium Oxide)
- When K2O is dissolved in water, it reacts to form potassium hydroxide (KOH):
\[ K2O + H2O \rightarrow 2 KOH \]
- KOH is a strong base. Therefore, K2O is a base when dissolved in water.

**Hint:** Strong bases produce hydroxide ions (OH⁻) in solution.

### Step 2: Analyze Na2O2 (Sodium Peroxide)
- When Na2O2 is dissolved in water, it reacts to form sodium hydroxide (NaOH) and hydrogen peroxide (H2O2):
\[ Na2O2 + 2 H2O \rightarrow 2 NaOH + H2O2 \]
- NaOH is a strong base, and H2O2 is a weak acid. The presence of NaOH indicates that Na2O2 is also a base when dissolved.

**Hint:** Look for the formation of hydroxide ions to identify bases.

### Step 3: Analyze NO2 (Nitrogen Dioxide)
- When NO2 is dissolved in water, it reacts to form nitric acid (HNO3) and nitrous acid (HNO2):
\[ 2 NO2 + H2O \rightarrow HNO3 + HNO2 \]
- Both HNO3 and HNO2 are acids (HNO3 is a strong acid, and HNO2 is a weak acid). Therefore, NO2 does not produce a base when dissolved.

**Hint:** Acids produce H⁺ ions in solution, leading to a lower pH.

### Step 4: Analyze Cl2O7 (Dichlorine Heptoxide)
- When Cl2O7 is dissolved in water, it reacts to form perchloric acid (HClO4):
\[ Cl2O7 + H2O \rightarrow 2 HClO4 \]
- HClO4 is a very strong acid. Thus, Cl2O7 does not produce a base when dissolved.

**Hint:** Strong acids will lower the pH of the solution, indicating that no basic properties are present.

### Conclusion
From the analysis:
- **K2O** and **Na2O2** are bases when dissolved in water.
- **NO2** and **Cl2O7** do not produce bases; instead, they produce acids.

### Final Answer
The compounds that are not bases when dissolved are **NO2** and **Cl2O7**.