The molecule which is pyramidal in shape is

Options

A. `PCl_(3)`
B. `CO_(3) ^(2-)`
C. `SO_(3)`
D. `NO_(2)^(-)`

Answer

To determine which molecule is pyramidal in shape, we will analyze the molecular geometry of several options based on their valence electrons, bond pairs, and lone pairs.

### Step 1: Identify the Valence Electrons
- **PCl3 (Phosphorus Trichloride)**:
- Phosphorus has 5 valence electrons.
- Chlorine has 7 valence electrons, but only 1 is used for bonding.
- Total for 3 Cl: 3 electrons from P and 3 from Cl = 6 electrons used in bonding.

### Step 2: Count Bond Pairs and Lone Pairs
- In PCl3:
- 3 bond pairs (P-Cl bonds).
- 2 electrons remain as lone pairs on phosphorus.

### Step 3: Determine the Steric Number
- Steric Number = Number of Bond Pairs + Number of Lone Pairs
- Steric Number for PCl3 = 3 (bond pairs) + 1 (lone pair) = 4.

### Step 4: Identify Hybridization
- With a steric number of 4, the hybridization is sp³.

### Step 5: Determine the Molecular Shape
- The presence of one lone pair and three bond pairs leads to a pyramidal shape (specifically, trigonal pyramidal).

### Conclusion
- **PCl3** is pyramidal in shape.

### Analyzing Other Molecules:
- **CO3²⁻ (Carbonate Ion)**:
- Steric number = 3 (trigonal planar).
- **SO3 (Sulfur Trioxide)**:
- Steric number = 3 (trigonal planar).
- **NO2⁻ (Nitrite Ion)**:
- Steric number = 3 (bent shape).

### Final Answer
The molecule that is pyramidal in shape is **PCl3**.

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