Which of the following polar solvents has the highest dielectric constant?

Options

A. `H_2O`
B. `D_2O`
C. `CH_3OH`
D. `C_2H_5OH`

Explanation

To determine which polar solvent has the highest dielectric constant, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Dielectric Constant**: The dielectric constant is a measure of a substance's ability to insulate charges from each other. It is influenced by the polarity of the molecules; higher polarity typically results in a higher dielectric constant.

2. **Identify the Polar Solvents**: The question mentions several polar solvents, including water (H2O), heavy water (D2O), methanol (CH3OH), and ethanol (C2H5OH).

3. **Evaluate the Polarity of Each Solvent**:
- **Water (H2O)**: Water has a significant difference in electronegativity between hydrogen and oxygen, leading to high polarity and strong hydrogen bonding.
- **Heavy Water (D2O)**: Heavy water is similar to water but has deuterium instead of hydrogen. It is slightly less polar than regular water.
- **Methanol (CH3OH)**: Methanol has a hydroxyl group (-OH) which provides some polarity, but it is less polar than water due to the presence of the carbon chain.
- **Ethanol (C2H5OH)**: Ethanol also has a hydroxyl group, but the longer carbon chain reduces its overall polarity compared to water and methanol.

4. **Compare Dielectric Constants**:
- Water (H2O): Approximately 82
- Heavy Water (D2O): Approximately 80.7
- Methanol (CH3OH): Approximately 35
- Ethanol (C2H5OH): Approximately 27

5. **Determine the Highest Dielectric Constant**: From the values above, water has the highest dielectric constant at approximately 82.

6. **Conclusion**: Therefore, the polar solvent with the highest dielectric constant is **water (H2O)**.

### Final Answer:
The polar solvent with the highest dielectric constant is **water (H2O)**.

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