Which of the following species contains three bond pairs and one lone pair around the central atom?

Options

A. `H_2O`
B. `BF_3`
C. `NH_2^-`
D. `PCl_3`

Explanation

To determine which of the given species contains three bond pairs and one lone pair around the central atom, we will analyze each molecule step by step.

### Step 1: Analyze H2O (Water)
- **Central Atom**: Oxygen (O)
- **Valence Electrons**: Oxygen has 6 valence electrons.
- **Bonds**: Oxygen forms 2 bond pairs with 2 hydrogen atoms.
- **Lone Pairs**: After forming 2 bonds, 4 electrons remain, which are arranged as 2 lone pairs.

**Conclusion**: H2O has 2 bond pairs and 2 lone pairs. Not our answer.

### Step 2: Analyze BF3 (Boron Trifluoride)
- **Central Atom**: Boron (B)
- **Valence Electrons**: Boron has 3 valence electrons.
- **Bonds**: Boron forms 3 bond pairs with 3 fluorine atoms.
- **Lone Pairs**: There are no remaining electrons; hence, there are no lone pairs.

**Conclusion**: BF3 has 3 bond pairs and 0 lone pairs. Not our answer.

### Step 3: Analyze NH2⁻ (Amide Ion)
- **Central Atom**: Nitrogen (N)
- **Valence Electrons**: Nitrogen has 5 valence electrons. The negative charge adds 1 more, giving a total of 6 electrons.
- **Bonds**: Nitrogen forms 2 bond pairs with 2 hydrogen atoms.
- **Lone Pairs**: After forming 2 bonds, 4 electrons remain, which are arranged as 2 lone pairs.

**Conclusion**: NH2⁻ has 2 bond pairs and 2 lone pairs. Not our answer.

### Step 4: Analyze PCl3 (Phosphorus Trichloride)
- **Central Atom**: Phosphorus (P)
- **Valence Electrons**: Phosphorus has 5 valence electrons.
- **Bonds**: Phosphorus forms 3 bond pairs with 3 chlorine atoms.
- **Lone Pairs**: After forming 3 bonds, 2 electrons remain, which are arranged as 1 lone pair.

**Conclusion**: PCl3 has 3 bond pairs and 1 lone pair. This is our answer.

### Final Answer:
The species that contains three bond pairs and one lone pair around the central atom is **PCl3**.

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