Which of the following molecules/ions has pyramidal shape?

Options

A. `SO_3`
B. `NH_4^+`
C. `PCl_3`
D. `H_2O`

Answer

To determine which of the given molecules or ions has a pyramidal shape, we will analyze the molecular geometry of each option provided.

### Step-by-Step Solution:

1. **Identify the molecules/ions given:**
- SO3 (Sulfur Trioxide)
- NH4+ (Ammonium ion)
- PCl3 (Phosphorus Trichloride)
- H2O (Water)

2. **Analyze SO3:**
- SO3 has a central sulfur atom surrounded by three oxygen atoms.
- The electron geometry is trigonal planar due to the three bonding pairs and no lone pairs on the sulfur atom.
- **Shape:** Trigonal planar.

3. **Analyze NH4+:**
- NH4+ has a central nitrogen atom bonded to four hydrogen atoms.
- There are no lone pairs on the nitrogen atom, leading to a tetrahedral shape.
- **Shape:** Tetrahedral.

4. **Analyze PCl3:**
- PCl3 has a central phosphorus atom bonded to three chlorine atoms and has one lone pair of electrons on the phosphorus atom.
- The presence of the lone pair causes the shape to be trigonal pyramidal.
- **Shape:** Trigonal pyramidal.

5. **Analyze H2O:**
- H2O has a central oxygen atom bonded to two hydrogen atoms and has two lone pairs of electrons.
- The shape of water is bent due to the two lone pairs.
- **Shape:** Bent.

6. **Conclusion:**
- Among the given options, only PCl3 has a trigonal pyramidal shape.

### Final Answer:
The molecule with a pyramidal shape is **PCl3**.

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