Which of the followig reaction is not a ion-exchange reaction?

Options

A. `Pb(NO_(3))_(2)+2KItoPbI_(2)darr+2KNO_(3)`
B. `KNO_(2)+AgFtoAgNO_(2)darr+KF`
C. `2AgF+MgCl_(2)toMgF_(2)darr+2AgCldarr`
D. `CaSO_(3)(ppt)+SO_(2)+H_(2)OtoCa(HSO_(3))_(2)`

Explanation

To determine which of the following reactions is not an ion-exchange reaction, we first need to understand what an ion-exchange reaction entails. In an ion-exchange reaction, ions from two different compounds swap places to form new compounds.

### Step-by-Step Solution:

1. **Understand Ion-Exchange Reactions**:
- In an ion-exchange reaction, cations and anions from two ionic compounds exchange partners. For example, if we have two ionic compounds, A+X- and B+Y-, the exchange would result in A+Y- and B+X-.

2. **Analyze the Given Options**:
- We need to look at each option provided and determine if they involve the exchange of ions.

3. **Option A**: Lead Nitrate Reaction
- The reaction involves lead ions (Pb2+) and nitrate ions (NO3-), forming PbI2. Here, the nitrate ions are replaced by iodide ions (I-). This is an ion-exchange reaction.

4. **Option B**: Nitrite and Fluoride Reaction
- In this reaction, nitrite ions (NO2-) are replaced by fluoride ions (F-). This is also an ion-exchange reaction.

5. **Option C**: Chloride Ion Reaction
- Here, chloride ions (Cl-) are exchanged, forming AgCl and MgF2. This is again an ion-exchange reaction.

6. **Option D**: Combination Reaction
- In this case, three reactant molecules combine to form a single product without any ions being exchanged. This is a combination reaction, not an ion-exchange reaction.

7. **Conclusion**:
- Since option D is the only one that does not involve the exchange of ions, it is the correct answer.

### Final Answer:
The reaction that is not an ion-exchange reaction is **Option D**.