Number of possible reactions out of the following is
`Cu+2AgNO_(3) to 2Ag+Cu(NO_(3))_(2)`
`Cu+ZnSO_(4)toCuSO_(4)+Zn`
`Mg+CuSO_(4) to MgSO_(4)+Cu`
`Zn+PbSO_(4) to ZnSO_(4)+Pb`

Explanation

To determine the number of possible reactions from the given equations, we need to analyze each reaction based on the reactivity series of metals. The reactivity series ranks metals from most reactive to least reactive, which helps us predict whether a displacement reaction will occur.

### Step-by-Step Solution:

1. **Identify the Reactions:**
- Reaction 1: \( \text{Cu} + 2\text{AgNO}_3 \rightarrow 2\text{Ag} + \text{Cu(NO}_3)_2 \)
- Reaction 2: \( \text{Cu} + \text{ZnSO}_4 \rightarrow \text{CuSO}_4 + \text{Zn} \)
- Reaction 3: \( \text{Mg} + \text{CuSO}_4 \rightarrow \text{MgSO}_4 + \text{Cu} \)
- Reaction 4: \( \text{Zn} + \text{PbSO}_4 \rightarrow \text{ZnSO}_4 + \text{Pb} \)

2. **Analyze Each Reaction:**
- **Reaction 1:** Copper (Cu) is more reactive than Silver (Ag). Therefore, this reaction is possible.
- **Reaction 2:** Copper (Cu) is less reactive than Zinc (Zn). Therefore, this reaction will not occur.
- **Reaction 3:** Magnesium (Mg) is more reactive than Copper (Cu). Therefore, this reaction is possible.
- **Reaction 4:** Zinc (Zn) is more reactive than Lead (Pb). Therefore, this reaction is possible.

3. **Count the Possible Reactions:**
- Possible reactions: Reaction 1, Reaction 3, and Reaction 4.
- Not possible: Reaction 2.
- Total possible reactions = 3.

### Final Answer:
The number of possible reactions is **3**.