The number of weak electrolytes among the following is
`CH_(3)CO O Na, H_(2)CO_(3),
HCO O H,
C_(2)H_(5)HN_(2),
Na_(2)CO_(3),
Ca(OH)_(2),
CH_(3)CO ONH_(4),
HNO_(2),
HI and HF`.

Explanation

To determine the number of weak electrolytes among the given compounds, we need to classify each compound as either a strong electrolyte or a weak electrolyte. Here's how we can do that step by step:

### Step 1: Understand the definitions
- **Strong Electrolytes**: These are substances that completely dissociate into ions when dissolved in water. Examples include strong acids, strong bases, and soluble salts.
- **Weak Electrolytes**: These substances only partially dissociate into ions in solution. Examples include weak acids and weak bases.

### Step 2: Analyze each compound
1. **CH₃COONa (Sodium Acetate)**: This is a salt formed from a strong base (NaOH) and a weak acid (acetic acid). It is considered a strong electrolyte because it completely dissociates in solution.

2. **H₂CO₃ (Carbonic Acid)**: This is a weak acid and only partially dissociates in water, making it a weak electrolyte.

3. **HCOOH (Formic Acid)**: This is also a weak acid and partially dissociates in water, so it is a weak electrolyte.

4. **C₂H₅NH₂ (Ethylamine)**: This is a weak base and does not completely dissociate in water, classifying it as a weak electrolyte.

5. **Na₂CO₃ (Sodium Carbonate)**: This salt completely dissociates in water, thus it is a strong electrolyte.

6. **Ca(OH)₂ (Calcium Hydroxide)**: Although it is a base, it is considered a strong electrolyte because it dissociates significantly in water.

7. **CH₃COONH₄ (Ammonium Acetate)**: This salt dissociates completely in water, making it a strong electrolyte.

8. **HNO₂ (Nitrous Acid)**: This is a weak acid and partially dissociates in water, so it is a weak electrolyte.

9. **HI (Hydroiodic Acid)**: This is a strong acid and completely dissociates in water, classifying it as a strong electrolyte.

10. **HF (Hydrofluoric Acid)**: This is a weak acid and only partially dissociates in water, making it a weak electrolyte.

### Step 3: Count the weak electrolytes
From the analysis:
- Weak electrolytes: H₂CO₃, HCOOH, C₂H₅NH₂, HNO₂, HF
- Total weak electrolytes = 5

### Final Answer
The number of weak electrolytes among the given compounds is **5**.

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