Transition elements form binary compounds with halogens. Which of the following elements will form `MF_(3)` type compounds?

Options

A. 1. Cr
B. 2. Cu
C. 3. Ni
D. 4. All of these.

Answer

To determine which transition element will form `MF3` type compounds, we need to analyze the electronic configurations of the given elements and their ability to lose or share electrons.

### Step-by-Step Solution:

1. **Understanding MF3 Compounds**:
- The formula `MF3` indicates that the metal (M) can form three bonds with fluorine (F). This typically means that the metal must be able to lose or share three electrons.

2. **Identifying the Elements**:
- The elements provided are chromium (Cr), copper (Cu), and nickel (Ni). We need to analyze their electronic configurations.

3. **Electronic Configurations**:
- **Chromium (Cr)**: Atomic number 24
- Electronic configuration: [Ar] 3d^5 4s^1
- **Copper (Cu)**: Atomic number 29
- Electronic configuration: [Ar] 3d^10 4s^1
- **Nickel (Ni)**: Atomic number 28
- Electronic configuration: [Ar] 3d^8 4s^2

4. **Analyzing the Ability to Form MF3**:
- **Chromium**:
- Chromium has 5 electrons in the 3d subshell and can lose 3 electrons (from 4s and 3d) to achieve a +3 oxidation state. Thus, it can form CrF3.
- **Copper**:
- Copper has a fully filled 3d subshell (3d^10) and typically does not lose three electrons easily. It usually forms +1 or +2 oxidation states, so it is less likely to form CuF3.
- **Nickel**:
- Nickel has 8 electrons in the 3d subshell and can lose 2 electrons (from 4s and 3d) to achieve a +2 oxidation state. It does not typically form a +3 oxidation state, so it is less likely to form NiF3.

5. **Conclusion**:
- Among the three elements, only chromium can effectively form `MF3` type compounds (specifically CrF3) due to its ability to attain a +3 oxidation state.

### Final Answer:
- The element that will form `MF3` type compounds is **Chromium (Cr)**.