Question

Which of the following molecules has a trigonal planar molecular geometry?

• A. NH₃
• B. BF₃
• C. H₂O
• D. CH₄

Hint:

Use VSEPR notation (AXₙEₘ) where A is the central atom, X is a bonding pair, and E is a lone pair to predict molecular shapes.

Answer 1

The Correct Option is B

To determine the molecular geometry using VSEPR theory, we follow these steps:

1. Identify the number of bonding pairs and lone pairs around the central atom for each molecule.
2. For NH₃ (ammonia): \[ \text{Nitrogen: 3 bonding pairs, 1 lone pair} \rightarrow \text{trigonal pyramidal (AX₃E)}. \]
3. For BF₃ (boron trifluoride): \[ \text{Boron: 3 bonding pairs, 0 lone pairs} \rightarrow \text{trigonal planar (AX₃)}. \]
4. For H₂O (water): \[ \text{Oxygen: 2 bonding pairs, 2 lone pairs} \rightarrow \text{bent (AX₂E₂)}. \]
5. For CH₄ (methane): \[ \text{Carbon: 4 bonding pairs, 0 lone pairs} \rightarrow \text{tetrahedral (AX₄)}. \]
6. Conclusion: Only BF₃ has a trigonal planar geometry.

Thus, the correct answer is: \[ \boxed{\text{BF}_3} \]