The ion most difficult to removes as precipitate is

Options

A. `Ag^(+)`
B. `NH_(4)^(+)`
C. `Fe^(+2)`
D. `Co^(+2)`

Answer

To determine which ion is the most difficult to remove as a precipitate among the given options (Ag+, NH4+, Fe2+, and Co2+), we can analyze the solubility and precipitation behavior of these ions.

### Step-by-Step Solution:

1. **Identify the Ions**: The ions provided are Ag+ (silver), NH4+ (ammonium), Fe2+ (iron), and Co2+ (cobalt).

2. **Understand Precipitation**: Precipitation occurs when ions in solution react to form an insoluble compound. The ease of precipitation depends on the solubility of the resulting compound.

3. **Analyze Each Ion**:
- **Ag+**: Silver ions can form precipitates with halides (like AgCl) and sulfides (like Ag2S), which are relatively insoluble.
- **NH4+**: Ammonium ions typically do not form insoluble precipitates with common anions. They remain soluble in water, making them difficult to remove as a precipitate.
- **Fe2+**: Iron ions can form precipitates, such as Fe(OH)2, which is insoluble under certain conditions.
- **Co2+**: Cobalt ions can also form precipitates, such as Co(OH)2, which can be removed from solution.

4. **Compare the Difficulty of Precipitation**:
- Among the ions, NH4+ is unique in that it does not readily form insoluble precipitates with common anions. This characteristic makes it the most difficult ion to remove from solution as a precipitate.

5. **Conclusion**: Based on the analysis, the ion that is most difficult to remove as a precipitate is **NH4+**.

### Final Answer:
The ion most difficult to remove as a precipitate is **NH4+**.

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