Which of the following species is /are capable of forming a coordinate bond with `BF_(3)` ?

Options

A. `PH_(3)`
B. `NH_(4)^(+)`
C. `OH^(-)`
D. `Mg^(2+)`

Answer

To determine which species are capable of forming a coordinate bond with BF3, we need to analyze the nature of BF3 and the given species.

### Step 1: Understand BF3
BF3 (Boron Trifluoride) is an electron-deficient molecule. It has three fluorine atoms bonded to a boron atom, and boron has only six electrons in its valence shell, making it electron-deficient. This characteristic classifies BF3 as a Lewis acid, which means it can accept electron pairs.

**Hint:** Remember that Lewis acids are electron acceptors.

### Step 2: Identify Electron-Rich Species
To form a coordinate bond with BF3, we need to find species that are electron-rich (Lewis bases) and can donate a pair of electrons.

### Step 3: Analyze the Given Species
1. **PH3 (Phosphine)**: Phosphorus has a lone pair of electrons and can act as a Lewis base. Therefore, PH3 can donate its lone pair to BF3, forming a coordinate bond.

2. **NH4+ (Ammonium ion)**: NH4+ has a positive charge and does not have any lone pairs to donate. It is electron-deficient, thus cannot form a coordinate bond with BF3.

3. **OH- (Hydroxide ion)**: The hydroxide ion has a lone pair of electrons and is negatively charged, making it electron-rich. It can donate its lone pair to BF3, forming a coordinate bond.

4. **Mg2+ (Magnesium ion)**: Mg2+ is a cation and is electron-deficient. It cannot donate electrons to BF3, so it cannot form a coordinate bond.

### Step 4: Conclusion
From the analysis, the species capable of forming a coordinate bond with BF3 are:
- PH3
- OH-

Thus, the correct answer is PH3 and OH-.

**Final Answer:** PH3 and OH- are capable of forming a coordinate bond with BF3.