A: When 4 moles of `H_(2)` reacts with 2 moles of `O_(2)`, then 4. moles of water is formed.
R: `O_(2)` will act as limiting reagent.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion
C. If Assertion is true statement but Reason is false
D. If both Assertion and Reason are false statements

Answer

To solve the problem, we need to analyze the chemical reaction between hydrogen (H₂) and oxygen (O₂) to form water (H₂O). The balanced chemical equation for this reaction is:

\[ 2H_2 + O_2 \rightarrow 2H_2O \]

### Step-by-Step Solution:

1. **Identify the Balanced Reaction:**
The balanced equation shows that 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

2. **Determine the Moles of Reactants:**
According to the question:
- Moles of H₂ = 4 moles
- Moles of O₂ = 2 moles

3. **Calculate the Stoichiometric Ratio:**
From the balanced equation, we see that:
- 2 moles of H₂ react with 1 mole of O₂.
- Therefore, 4 moles of H₂ would require \( \frac{4 \text{ moles H₂}}{2 \text{ moles H₂/mole O₂}} = 2 \text{ moles O₂} \).

4. **Identify the Limiting Reagent:**
Since we have exactly 2 moles of O₂ available, which is exactly what is needed to react with 4 moles of H₂, we can conclude:
- Both reactants will be completely consumed in the reaction.
- However, since we are using all of the available O₂, it is the limiting reagent.

5. **Calculate the Amount of Product Formed:**
According to the balanced equation, 2 moles of H₂ and 1 mole of O₂ produce 2 moles of H₂O. Therefore, if we start with 4 moles of H₂ and 2 moles of O₂:
- The amount of water produced will be \( 2 \times 2 = 4 \text{ moles of H₂O} \).

6. **Conclusion:**
The assertion states that when 4 moles of H₂ react with 2 moles of O₂, 4 moles of water is formed, which is true. The reason states that O₂ will act as the limiting reagent, which is also true because it is the reactant that will be completely consumed first.

### Final Answer:
Both the assertion and the reason are true, making the statement correct.