Conc. `H_2 SO_4` reacts with four moles of `Ag` to give ____ moles of `Ag_2 SO_4`.

Explanation

To solve the problem of how many moles of `Ag2SO4` are produced when concentrated `H2SO4` reacts with 4 moles of `Ag`, we can follow these steps:

### Step 1: Write the balanced chemical equation
The first step is to write the balanced chemical equation for the reaction between silver (`Ag`) and concentrated sulfuric acid (`H2SO4`).

The reaction can be represented as:
\[ 2 \, Ag + H2SO4 \rightarrow Ag2SO4 + H2O + SO2 \]

### Step 2: Analyze the stoichiometry
From the balanced equation, we can see that:
- 2 moles of `Ag` react with 1 mole of `H2SO4` to produce 1 mole of `Ag2SO4`.

### Step 3: Determine the amount of `Ag2SO4` produced from 4 moles of `Ag`
Since the reaction shows that 2 moles of `Ag` produce 1 mole of `Ag2SO4`, we can set up a proportion to find out how many moles of `Ag2SO4` will be produced from 4 moles of `Ag`.

Using the stoichiometric ratio:
- If 2 moles of `Ag` produce 1 mole of `Ag2SO4`, then 4 moles of `Ag` will produce:
\[ \text{Moles of } Ag2SO4 = \frac{4 \, \text{moles of } Ag}{2 \, \text{moles of } Ag} \times 1 \, \text{mole of } Ag2SO4 = 2 \, \text{moles of } Ag2SO4 \]

### Step 4: Conclusion
Thus, when concentrated `H2SO4` reacts with 4 moles of `Ag`, it produces **2 moles of `Ag2SO4`**.

### Final Answer:
**2 moles of `Ag2SO4`**

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