In the reaction `ROH overset("Red" P + I_2)(rarr)RI + A`, A is :

Options

A. `H_3PO_2`
B. `H_3PO_3`
C. `H_3PO_6`
D. `HPO_3`

Explanation

To solve the question regarding the reaction of alcohol (ROH) with red phosphorus and iodine (I2) to produce alkyl iodide (RI) and another product A, we can follow these steps:

### Step 1: Identify the Reactants and Products
The reactants are alcohol (ROH), red phosphorus (P), and iodine (I2). The products are alkyl iodide (RI) and another compound A.

**Hint:** Recognize that the reaction involves the conversion of alcohol to alkyl iodide.

### Step 2: Understand the Reaction Mechanism
When alcohol reacts with red phosphorus and iodine, it first forms phosphorus triiodide (PI3). This intermediate then reacts with the alcohol.

**Hint:** Remember that red phosphorus and iodine can form phosphorus triiodide, which is crucial in the reaction.

### Step 3: Determine the Stoichiometry
For every 1 mole of alcohol that reacts, 1 mole of alkyl iodide is produced. If 3 moles of alcohol are used, then 3 moles of alkyl iodide will be formed.

**Hint:** Keep track of the number of moles of reactants and products to understand what remains after the reaction.

### Step 4: Identify the Byproducts
In the process, the red phosphorus and iodine will react with the alcohol, leading to the formation of alkyl iodide and leaving behind some byproducts. The reaction will also produce hydrogen gas (H2) and phosphorous acid (H3PO3).

**Hint:** Think about what elements are left after the formation of alkyl iodide and how they combine to form other compounds.

### Step 5: Write the Final Equation
The balanced equation for the reaction can be summarized as follows:
- 3 ROH + PI3 → 3 RI + H3PO3 + 3 H2

From this, we can see that the byproduct A is phosphorous acid (H3PO3).

**Hint:** Check the final products to confirm the identity of A based on the leftover elements.

### Conclusion
Thus, the product A in the reaction is **H3PO3** (phosphorous acid).

**Final Answer:** A is H3PO3.