Which of the following is polar ? .

Options

A. `NF_(3)`
B. `BF_(3)`
C. `SF_(6)`
D. `SiF_(4)`

Explanation

To determine which of the given molecules is polar, we need to analyze the molecular geometry and the electronegativity of the atoms involved in each molecule. Here's a step-by-step solution:

### Step 1: Analyze NF3 (Nitrogen Trifluoride)
- **Structure**: NF3 has a nitrogen atom at the center with three fluorine atoms attached and one lone pair of electrons on nitrogen.
- **Electronegativity**: Fluorine is more electronegative than nitrogen, which means the bond moments (dipoles) point towards the fluorine atoms.
- **Lone Pair**: The lone pair on nitrogen also contributes to the molecular dipole moment, pointing away from nitrogen.
- **Net Dipole Moment**: The bond dipoles do not cancel out due to the presence of the lone pair, resulting in a net dipole moment.
- **Conclusion**: NF3 is a polar molecule.

### Step 2: Analyze BF3 (Boron Trifluoride)
- **Structure**: BF3 has a boron atom at the center with three fluorine atoms arranged in a trigonal planar geometry.
- **Electronegativity**: The bond moments point towards the fluorine atoms.
- **Symmetry**: The geometry is symmetrical, and the bond dipoles cancel each other out.
- **Net Dipole Moment**: The net dipole moment is zero.
- **Conclusion**: BF3 is a nonpolar molecule.

### Step 3: Analyze SF6 (Sulfur Hexafluoride)
- **Structure**: SF6 has a sulfur atom at the center with six fluorine atoms in a square bipyramidal arrangement.
- **Electronegativity**: The bond moments point towards the fluorine atoms.
- **Symmetry**: The symmetrical arrangement means that the bond dipoles cancel each other out.
- **Net Dipole Moment**: The net dipole moment is zero.
- **Conclusion**: SF6 is a nonpolar molecule.

### Step 4: Analyze SiF4 (Silicon Tetrafluoride)
- **Structure**: SiF4 has a silicon atom at the center with four fluorine atoms arranged in a tetrahedral geometry.
- **Electronegativity**: The bond moments point towards the fluorine atoms.
- **Symmetry**: The tetrahedral shape allows for the bond dipoles to cancel each other out.
- **Net Dipole Moment**: The net dipole moment is zero.
- **Conclusion**: SiF4 is a nonpolar molecule.

### Final Conclusion
After analyzing all four molecules:
- **Polar Molecule**: NF3
- **Nonpolar Molecules**: BF3, SF6, SiF4

Thus, the answer to the question "Which of the following is polar?" is **NF3**.

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