Dipole-dipole (Keesom) attraction is present in :-

Options

A. `KCl+H_(2)O`
B. `CH_(3)-underset(O)underset(||)C-CH_(3)+CH_(3)-C-=N`
C. `NO_(3)^(-) +Cl_(2)`
D. `HCl +Cl_(2)`

Explanation

To determine where dipole-dipole (Keesom) attraction is present, we need to analyze the nature of the molecules involved in each option. Dipole-dipole interactions occur between polar molecules, where the positive end of one molecule is attracted to the negative end of another.

### Step-by-Step Solution:

1. **Understand Dipole-Dipole Interactions**:
- Dipole-dipole interactions occur in polar molecules. A polar molecule has a permanent dipole moment due to the difference in electronegativity between the atoms, leading to a partial positive charge (δ+) on one end and a partial negative charge (δ-) on the other end.

2. **Analyze Each Option**:
- **Option A: KCl + H2O**:
- KCl is an ionic compound, while H2O is a polar molecule. The interaction between an ion and a polar molecule is classified as ion-dipole interaction, not dipole-dipole.

- **Option B: Acetone (CH3C(=O)CH3) + Acetonitrile (CH3CN)**:
- Both acetone and acetonitrile are polar molecules. Acetone has a carbonyl group (C=O) which creates a dipole, and acetonitrile has a nitrile group (C≡N) that is also polar. Therefore, dipole-dipole interactions will occur between these two molecules.

- **Option C: NO3^- + Cl2**:
- NO3^- (nitrate ion) is polar due to its charge distribution, while Cl2 is a non-polar molecule. The interaction here would be classified as dipole-induced dipole interaction, not dipole-dipole.

- **Option D: Cl + Cl2**:
- Cl is a polar molecule (Cl2 is non-polar). The interaction between a polar molecule and a non-polar molecule is also classified as dipole-induced dipole interaction.

3. **Conclusion**:
- The only pair that exhibits dipole-dipole interactions is **Option B: Acetone + Acetonitrile**.

### Final Answer:
Dipole-dipole (Keesom) attraction is present in **Option B: Acetone + Acetonitrile**.