How many compounds have zero dipole-moment ?
(a)`CH_3Cl` , (b)`CHCl_5` , ( c)`C Cl_4` , (d)`CH_3OH`
(e)`CH_3OCH_3` , (f)`CO_2` , (g)`CH_4` , (h)`CH_3COCH_3`

Explanation

To determine how many compounds have a zero dipole moment from the given options, we will analyze each compound based on its molecular geometry and the electronegativity of its atoms.

### Step-by-Step Solution:

1. **CH₃Cl (Methyl Chloride)**:
- Structure: Tetrahedral
- Chlorine is more electronegative than carbon, creating a dipole moment.
- **Result**: Not zero.

2. **CHCl₃ (Chloroform)**:
- Structure: Tetrahedral
- Chlorine atoms create a dipole moment due to their electronegativity.
- **Result**: Not zero.

3. **CCl₄ (Carbon Tetrachloride)**:
- Structure: Tetrahedral
- The molecule is symmetrical, and the dipole moments of the C-Cl bonds cancel each other out.
- **Result**: Zero dipole moment.

4. **CH₃OH (Methanol)**:
- Structure: Bent
- Oxygen is more electronegative, leading to a net dipole moment.
- **Result**: Not zero.

5. **CH₃OCH₃ (Dimethyl Ether)**:
- Structure: Bent
- The dipole moments do not cancel due to the asymmetrical arrangement.
- **Result**: Not zero.

6. **CO₂ (Carbon Dioxide)**:
- Structure: Linear
- The dipole moments of the C=O bonds cancel each other due to symmetry.
- **Result**: Zero dipole moment.

7. **CH₄ (Methane)**:
- Structure: Tetrahedral
- The molecule is symmetrical, and the dipole moments cancel out.
- **Result**: Zero dipole moment.

8. **CH₃COCH₃ (Acetone)**:
- Structure: Trigonal planar around the carbonyl carbon.
- The electronegative oxygen creates a dipole moment that does not cancel.
- **Result**: Not zero.

### Summary of Results:
- Compounds with zero dipole moment: **CCl₄, CO₂, CH₄**
- Total number of compounds with zero dipole moment: **3**

### Final Answer:
**3 compounds have zero dipole moment.**

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