Which one of the following pairs do not impart colour to the flame?

Options

A. `BeCl_(2) and SrCl_(2)`
B. `BeCl_(2) and MgCl_(2)`
C. `CaCl_(2) and BaCl_(2)`
D. `BaCl_(2) and SrCl_(2)`

Answer

To determine which pair of compounds does not impart color to the flame, we need to analyze the flame test results for the given compounds. The compounds in question are chloride salts of the alkaline earth metals from Group 2: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds we are considering are Beryllium chloride (BeCl2), Magnesium chloride (MgCl2), Calcium chloride (CaCl2), Strontium chloride (SrCl2), and Barium chloride (BaCl2).

2. **Understand Flame Test**: The flame test is a qualitative analysis technique used to identify the presence of certain metal ions based on the color they emit when heated in a flame. Different metal ions produce characteristic colors.

3. **Analyze Each Compound**:
- **Beryllium Chloride (BeCl2)**: Does not impart color to the flame.
- **Magnesium Chloride (MgCl2)**: Does not impart color to the flame.
- **Calcium Chloride (CaCl2)**: Imparts a brick red color to the flame.
- **Strontium Chloride (SrCl2)**: Imparts a red color to the flame.
- **Barium Chloride (BaCl2)**: Imparts an apple green color to the flame.

4. **Conclusion**: From the analysis, we find that Beryllium chloride and Magnesium chloride do not impart any color to the flame. This is due to their small ionic size and high ionization enthalpy, which means their electrons are tightly bound and cannot be excited by the heat of the flame.

5. **Final Answer**: The pair that does not impart color to the flame is **Beryllium chloride (BeCl2) and Magnesium chloride (MgCl2)**.