How many oxides are soluble in moderaterly concentrated aqueous solution of NaOH.
`{:(SO_3",",Cl_2O_7",",N_2O_5",",CO),((1),(2),(3),"(4)"),(K_2O",",Cr_2O_3",",BaO",",GeO_2),((5),(6),(7),"(8)"):}`

Explanation

To determine how many oxides are soluble in moderately concentrated aqueous solutions of NaOH, we will analyze each oxide given in the question.

### Step-by-Step Solution:

1. **Identify the Oxides**: The oxides provided are:
- SO₃
- Cl₂O₇
- N₂O₅
- CO
- K₂O
- Cr₂O₃
- BaO
- GeO₂

2. **Classify the Oxides**: We classify these oxides into acidic, basic, and neutral:
- **Acidic Oxides**: SO₃, Cl₂O₇, N₂O₅, GeO₂
- **Basic Oxides**: K₂O, BaO
- **Neutral Oxide**: CO

3. **Reactions with NaOH**:
- **SO₃**:
- Reaction: SO₃ + 2 NaOH → Na₂SO₄ + H₂O
- Conclusion: Soluble in NaOH.
- **Cl₂O₇**:
- Reaction: Cl₂O₇ + 2 NaOH → 2 NaClO₄ + H₂O
- Conclusion: Soluble in NaOH.
- **N₂O₅**:
- Reaction: N₂O₅ + 2 NaOH → 2 NaNO₃ + H₂O
- Conclusion: Soluble in NaOH.
- **CO**:
- Reaction: No reaction with NaOH (neutral oxide).
- Conclusion: Not soluble in NaOH.
- **K₂O**:
- Reaction: K₂O + H₂O → 2 KOH
- Conclusion: Soluble in NaOH (as it forms KOH).
- **Cr₂O₃**:
- Reaction: Cr₂O₃ + 2 NaOH + 3 H₂O → 2 NaCr(OH)₄
- Conclusion: Soluble in NaOH (amphoteric oxide).
- **BaO**:
- Reaction: BaO + H₂O → Ba(OH)₂
- Conclusion: Soluble in NaOH (as it forms Ba(OH)₂).
- **GeO₂**:
- Reaction: GeO₂ + 2 NaOH + 3 H₂O → Na₂GeO₃ + H₂O
- Conclusion: Soluble in NaOH.

4. **Count the Soluble Oxides**:
- The soluble oxides are: SO₃, Cl₂O₇, N₂O₅, K₂O, Cr₂O₃, BaO, and GeO₂.
- The only oxide that is not soluble is CO.

5. **Final Answer**:
- Total number of oxides soluble in moderately concentrated aqueous solution of NaOH = 7.