Which of the following is not correct for `D_2 O` ?

Options

A. Boiling point is higher than `H_2O`
B. `D_2O` reacts slowly than `H_2O`
C. Viscosity is higher than `H_2O ` at `25^@` C
D. Solubility of NaCl in it is more than `H_2O`

Answer

To determine which statement is not correct regarding D₂O (heavy water), we can analyze the properties of D₂O in comparison to H₂O (regular water).

### Step-by-Step Solution:

1. **Understanding D₂O**:
- D₂O is known as heavy water, which contains deuterium (D), an isotope of hydrogen that has one neutron, compared to protium (H), which has no neutrons.
- The molecular formula D₂O indicates that it consists of two deuterium atoms and one oxygen atom.

2. **Boiling Point Comparison**:
- The boiling point of D₂O is higher than that of H₂O. This is due to the stronger hydrogen bonding in D₂O, which results from the increased mass and size of deuterium compared to protium.
- **Conclusion**: This statement is correct.

3. **Reactivity**:
- D₂O reacts more slowly than H₂O. The presence of the additional neutron in deuterium increases the mass and size of the molecule, which affects its reactivity.
- **Conclusion**: This statement is correct.

4. **Viscosity**:
- Viscosity is a measure of a fluid's resistance to flow. D₂O has a higher viscosity than H₂O due to stronger intermolecular forces (hydrogen bonds) resulting from the presence of deuterium.
- **Conclusion**: This statement is correct.

5. **Solubility of NaCl**:
- The solubility of NaCl in D₂O is actually less than in H₂O. The stronger D-O bonds in D₂O lead to decreased solvation of ions, which means that NaCl does not dissolve as well in D₂O compared to H₂O.
- **Conclusion**: This statement is incorrect.

### Final Answer:
The statement that is not correct for D₂O is that the solubility of NaCl in D₂O is more than in H₂O.