Between ionic and covalent bonds, there are large majority of bonds, in which the bonding electrons are shared unequally between two atoms but are not completely transferred.Such bonds are said to be polar covalent bonds and the bond polarity is due to difference in electronegativity, the ability of an atom in a molecule to attract the shared electrons in a covalent bond.
The measure of net polarity is a quantity called the dipole moment, `mu` , which is defined as the magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges : `mu=Qxxr`.Molecular polarities give rise to some of the forces that occur between molecules and these forces are of several different types including dipole-dipole forces, London dispersion forces, and hydrogen bonds. All these intermolecular forces are electrical in origin and result from the mutual attraction of unlike charges or the mutual repulsion of like charges.
Which of the following statement is true ?

Options

A. The dipole moment of `NF_3` is more than `NH_3`
B. trans-2,3-dichloro-2-pentene does not have net permanent dipole moment
C. Carbon tetrachloride has no net dipole moment because of its regular tetrahedral structure
D. Dipole moment is zero for sulphurdioxide molecule.

Explanation

To solve the question regarding the true statement among the given options related to dipole moments and molecular polarity, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Polar Covalent Bonds**:
- Polar covalent bonds occur when electrons are shared unequally between two atoms due to differences in electronegativity.
- The dipole moment (μ) quantifies the polarity of a molecule and is given by the formula:
\[ \mu = Q \times r \]
where \( Q \) is the magnitude of the charge and \( r \) is the distance between the charges.

2. **Analyzing the First Statement**:
- **Statement**: The dipole moment of NF3 is more than that of NH3.
- **Analysis**:
- NH3 (Ammonia) has a lone pair on nitrogen, making it polar with a dipole moment directed towards the nitrogen.
- NF3 (Nitrogen trifluoride) has a dipole moment directed towards fluorine, but the presence of the lone pair on nitrogen reduces the overall dipole moment.
- Conclusion: The dipole moment of NH3 is greater than that of NF3. Therefore, this statement is **incorrect**.

3. **Analyzing the Second Statement**:
- **Statement**: Trans-2,3-dichloro-2-pentene does not have a permanent dipole moment.
- **Analysis**:
- The molecule has two chlorine atoms that are symmetrically placed, which means their dipole moments cancel each other out.
- However, the presence of the CH3 and C2H5 groups creates an asymmetry in the molecule.
- Conclusion: This molecule does have a net dipole moment. Therefore, this statement is **incorrect**.

4. **Analyzing the Third Statement**:
- **Statement**: CCl4 (Carbon tetrachloride) has no net dipole moment because of its regular tetrahedral structure.
- **Analysis**:
- CCl4 has a symmetrical tetrahedral structure, and while the individual C-Cl bonds are polar, their dipole moments cancel each other out due to symmetry.
- Conclusion: This statement is **correct**.

5. **Analyzing the Fourth Statement**:
- **Statement**: The dipole moment is 0 for sulfur dioxide (SO2) molecule.
- **Analysis**:
- SO2 has a bent structure due to the presence of lone pairs on sulfur. The electronegativity difference between sulfur and oxygen leads to a net dipole moment directed towards the oxygen atoms.
- Conclusion: This statement is **incorrect**.

### Final Conclusion:
The only true statement among the options provided is:
- **CCl4 has no net dipole moment because of its regular tetrahedral structure.**