The electronegativities of four elements A, B, C, D are 4,3.17, 0.7 and 2.85 respectively and the electronegativities of hydrogen (H) and oxygen (O) atoms are 2.1 and 3.5 respectively.
Which of the following bonds is most polar? 

Options

A. B-C
B. A-D
C. B-D
D. C-D

Answer

To determine which bond is the most polar among the given options, we need to calculate the difference in electronegativities for each bond. The bond with the greatest difference in electronegativities will be the most polar.

### Step-by-Step Solution:

1. **Identify the Electronegativity Values**:
- Element A: 4
- Element B: 3.17
- Element C: 0.7
- Element D: 2.85
- Hydrogen (H): 2.1
- Oxygen (O): 3.5

2. **List the Bonds to Analyze**:
- B and C
- A and D
- B and D
- C and D

3. **Calculate the Difference in Electronegativity for Each Bond**:
- **For B and C**:
\[ |3.17 - 0.7| = 2.47 \]
- **For A and D**:
\[ |4 - 2.85| = 1.15 \]
- **For B and D**:
\[ |3.17 - 2.85| = 0.32 \]
- **For C and D**:
\[ |0.7 - 2.85| = 2.15 \]

4. **Compare the Differences**:
- B and C: 2.47
- A and D: 1.15
- B and D: 0.32
- C and D: 2.15

5. **Identify the Most Polar Bond**:
The bond with the highest difference in electronegativity is between B and C, which has a difference of 2.47.

### Conclusion:
The bond that is most polar is between **B and C**.

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