Due to high _______ of `H_2O, H_2O` has a very strong hydrating tendency.

Answer

To fill in the blank in the question "Due to high _______ of `H_2O, H_2O` has a very strong hydrating tendency," we need to identify the property of water that contributes to its ability to hydrate substances effectively.

### Step-by-Step Solution:

1. **Understanding Hydration**:
- Hydration refers to the process where water molecules surround and interact with solute particles, which can be ions or polar molecules. This interaction is crucial for dissolving substances in water.

2. **Identifying Key Properties of Water**:
- Water is known for its unique properties, one of which is its high dielectric constant. The dielectric constant is a measure of a substance's ability to insulate charges from each other.

3. **Relating Dielectric Constant to Hydration**:
- The high dielectric constant of water indicates that it can effectively reduce the electrostatic forces between charged particles (like ions). This property allows water to stabilize ions in solution, facilitating their solvation or hydration.

4. **Conclusion**:
- Therefore, the correct term to fill in the blank is "dielectric constant." The complete sentence reads: "Due to high dielectric constant of `H_2O`, `H_2O` has a very strong hydrating tendency."

### Final Answer:
Due to high **dielectric constant** of `H_2O`, `H_2O` has a very strong hydrating tendency.

---