Which of the following is a hypovalent molecule species?

Options

A. `NaF`
B. `COCl_(2)`
C. `NF_(4)^(+)`
D. `BeCl_(2)`

Explanation

To determine which of the following is a hypovalent molecule species, we need to analyze each option based on the number of valence electrons around the central atom after bonding. A hypovalent species is defined as one that has fewer than 8 electrons in its valence shell.

### Step-by-Step Solution:

1. **Understanding Hypovalent Species:**
- A hypovalent species is one that has less than 8 electrons in its valence shell after bonding.

2. **Analyzing Each Option:**
- **Option A: NaF**
- Sodium (Na) has 1 valence electron and fluorine (F) has 7 valence electrons.
- When Na donates its electron to F, Na becomes Na⁺ and F becomes F⁻.
- The resulting ion pair (Na⁺ and F⁻) does not form a molecule with a central atom that has fewer than 8 electrons.
- Thus, NaF is not hypovalent.

- **Option B: COCl₂**
- Carbon (C) has 4 valence electrons, and it forms two bonds with two chlorine atoms (Cl), each contributing 1 electron.
- The total number of electrons around carbon after bonding is 4 (from C) + 2 (from Cl) = 8.
- Therefore, COCl₂ is not hypovalent.

- **Option C: NF₄⁺**
- Nitrogen (N) has 5 valence electrons. The positive charge indicates that one electron is removed.
- Nitrogen forms four bonds with fluorine atoms, contributing 4 electrons.
- The total number of electrons around nitrogen is 4 (from N) + 4 (from F) = 8.
- Hence, NF₄⁺ is not hypovalent.

- **Option D: BeCl₂**
- Beryllium (Be) has 2 valence electrons and forms two bonds with two chlorine atoms.
- Each bond contributes 2 electrons (1 from Be and 1 from Cl).
- The total number of electrons around beryllium after bonding is 2 (from Be) + 2 (from Cl) = 4.
- Since 4 is less than 8, BeCl₂ is hypovalent.

3. **Conclusion:**
- The hypovalent species among the given options is **D: BeCl₂**.