Select the ion exchange reaction, which proceeds to forward direction in aqueous medium:

Options

A. `2AgCl+CaF_(2)overset("Aqueous")to2AgF+CaCl_(2)`
B. `BaSO_(4)+2NaOH overset("Aqueous")to Ba(OH)_(2)+Na_(2)SO_(4)`
C. `Pb(NO_(3))_(2)+2CH_(3)COONa overset("Aqueous")toPb(OA c)_(2)+2NaNO_(3)`
D. `Na_(2)CrO_(4)+BaCl_(2) overset("Aqueous ")to BaCrO_(4)+2NaCl`

Explanation

To solve the question regarding which ion exchange reaction proceeds in the forward direction in an aqueous medium, we will analyze each option based on the formation of precipitates and apply the Le Chatelier's principle.

### Step-by-Step Solution:

1. **Understand the Le Chatelier's Principle**:
- This principle states that if an equilibrium is disturbed, the system will shift in a direction that counteracts the disturbance. In terms of concentration, if the concentration of products increases, the equilibrium will shift towards the reactants, and vice versa.

2. **Identify the Reactions**:
- We need to evaluate the given reactions to see where a precipitate is formed in the forward direction.

3. **Evaluate Each Reaction**:
- **Reaction 1**:
\[ \text{AgCl (s) + CaF}_2 \rightarrow 2 \text{AgF (aq) + CaCl}_2 (aq) \]
- Here, AgCl is a precipitate. The reaction shifts backward because the precipitate is formed from the reactants.

- **Reaction 2**:
\[ \text{BaSO}_4 (s) + 2 \text{NaOH (aq)} \rightarrow \text{Ba(OH)}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \]
- BaSO4 is a precipitate. The reaction shifts backward for the same reason.

- **Reaction 3**:
\[ \text{Pb(NO}_3\text{)}_2 (aq) + 2 \text{CH}_3\text{COONa (aq)} \rightarrow \text{Pb(CH}_3\text{COO)}_2 (s) + 2 \text{NaNO}_3 (aq) \]
- Pb(NO3)2 is soluble, but Pb(CH3COO)2 is a precipitate. The reaction shifts backward.

- **Reaction 4**:
\[ \text{Na}_2\text{CrO}_4 (aq) + \text{BaCl}_2 (aq) \rightarrow \text{BaCrO}_4 (s) + 2 \text{NaCl (aq)} \]
- BaCrO4 is a precipitate formed in the forward direction. Therefore, the reaction proceeds forward.

4. **Conclusion**:
- The only reaction that forms a precipitate in the forward direction is Reaction 4. Thus, the correct answer is:
\[ \text{Na}_2\text{CrO}_4 (aq) + \text{BaCl}_2 (aq) \rightarrow \text{BaCrO}_4 (s) + 2 \text{NaCl (aq)} \]

### Final Answer:
**The ion exchange reaction that proceeds in the forward direction in aqueous medium is Reaction 4:**
\[ \text{Na}_2\text{CrO}_4 (aq) + \text{BaCl}_2 (aq) \rightarrow \text{BaCrO}_4 (s) + 2 \text{NaCl (aq)} \]