Question

Which one of the following molecules has the least dipole moment?

• A. H$_2$O
• B. BeF$_2$
• C. NH$_3$
• D. NF$_3$
• E. BF$_3$

Hint:

Perfect symmetry → zero dipole moment.

Answer 1

Answer: (E)

Concept: Dipole moment and molecular symmetry
---

Step 1: Key idea
Dipole moment depends on:
• polarity of bonds
• molecular symmetry ---

Step 2: Symmetrical molecules
If perfectly symmetric: \[ \mu = 0 \] ---

Step 3: Analyze BF$_3$

• Trigonal planar
• Symmetrical
• Dipoles cancel \[ \mu = 0 \] ---

Step 4: Others

• H$_2$O → bent → polar ❌
• NH$_3$ → pyramidal ❌
• NF$_3$ → polar ❌
• BeF$_2$ → linear (also zero but less emphasized) --- Final Answer: \[ \boxed{\text{BF}_3} \]