Which of the following ions can be separated by using `NH_(4)Cl` and `NH_(4)OH` ?

Options

A. `Fe^(3+) and Cr^(3+)`
B. `Cr^(3+) and Co^(2+)`
C. `Cr^(3+ and Al^(3+)`
D. `Al^(3+) and Ba^(2+)`

Answer

To determine which ions can be separated using ammonium chloride (NH₄Cl) and ammonium hydroxide (NH₄OH), we need to analyze the behavior of various cations when treated with these reagents.

### Step-by-Step Solution:

1. **Identify the Cations**: The given pairs of cations are:
- (i) Fe³⁺ and Cr³⁺
- (ii) Cr³⁺ and Co²⁺
- (iii) Cr³⁺ and Al³⁺
- (iv) Al³⁺ and Ba²⁺

2. **Understand the Group Reagents**: Ammonium chloride and ammonium hydroxide are used to precipitate certain cations. They are specifically used for the third group of cations in qualitative analysis, which includes Fe³⁺, Cr³⁺, and Al³⁺.

3. **Analyze Each Pair**:
- **Pair (i) Fe³⁺ and Cr³⁺**: Both Fe³⁺ and Cr³⁺ are third group cations. When treated with NH₄Cl and NH₄OH, both will precipitate as their hydroxides (Fe(OH)₃ and Cr(OH)₃). Therefore, they cannot be separated.

- **Pair (ii) Cr³⁺ and Co²⁺**: Cr³⁺ is a third group cation, while Co²⁺ is a fourth group cation. When treated with NH₄Cl and NH₄OH, only Cr³⁺ will precipitate as Cr(OH)₃, while Co²⁺ remains in solution. Thus, they can be separated.

- **Pair (iii) Cr³⁺ and Al³⁺**: Both Cr³⁺ and Al³⁺ are third group cations. When treated with NH₄Cl and NH₄OH, both will precipitate (Cr(OH)₃ and Al(OH)₃). Therefore, they cannot be separated.

- **Pair (iv) Al³⁺ and Ba²⁺**: Al³⁺ is a third group cation, while Ba²⁺ is a second group cation. When treated with NH₄Cl and NH₄OH, only Al³⁺ will precipitate as Al(OH)₃, while Ba²⁺ remains in solution. Thus, they can be separated.

4. **Conclusion**: The ions that can be separated using ammonium chloride and ammonium hydroxide are:
- Cr³⁺ and Co²⁺
- Al³⁺ and Ba²⁺

### Final Answer:
The ions that can be separated using NH₄Cl and NH₄OH are:
- (ii) Cr³⁺ and Co²⁺
- (iv) Al³⁺ and Ba²⁺