Strong reducing behaviour of `H_(3)PO_(2)` is due to

Options

A. 1. low oxidation state of phosphorus
B. 2. presence of two - OH groups and one P-H bond
C. 3. presence of one - OH group and two P-H bonds
D. 4. high electron gain enthalpy of phosphorus.

Explanation

To determine the strong reducing behavior of \( H_3PO_2 \) (phosphorous acid), we can analyze the structure and the bonding of the molecule. Here’s a step-by-step solution:

### Step 1: Structure of \( H_3PO_2 \)
- The molecular structure of \( H_3PO_2 \) consists of one phosphorus atom (P) bonded to three hydrogen atoms (H) and one oxygen atom (O) that is also bonded to a hydrogen atom (forming a hydroxyl group, -OH).
- The structural formula can be represented as \( H_2P(OH) \).

### Step 2: Identify the Bonds
- In \( H_3PO_2 \), there are two types of bonds involving phosphorus:
- Two P-H bonds (phosphorus-hydrogen bonds).
- One P-O bond (with the oxygen also bonded to a hydrogen atom, forming the hydroxyl group).

### Step 3: Analyzing Reducing Behavior
- A reducing agent is a substance that can donate electrons or hydrogen ions (H+) to another substance.
- The presence of the P-H bonds indicates that phosphorus has the ability to release hydrogen, which is crucial for its reducing behavior.

### Step 4: Evaluating the Options
- Now, let’s evaluate the provided options:
1. **Low oxidation state of phosphorus**: While phosphorus in \( H_3PO_2 \) is in a lower oxidation state compared to other phosphorus oxoacids, this alone does not explain the strong reducing behavior.
2. **Presence of 2 OH groups and 1 P-H bond**: This is incorrect as there is only one OH group.
3. **Presence of 1 OH group and 2 P-H bonds**: This is correct as it accurately describes the structure and the ability of \( H_3PO_2 \) to release hydrogen.
4. **High electron gain enthalpy of phosphorus**: This is not relevant to the reducing behavior of \( H_3PO_2 \).

### Conclusion
- The strong reducing behavior of \( H_3PO_2 \) is primarily due to the presence of one OH group and two P-H bonds, which allows it to donate hydrogen easily.

### Final Answer
- The correct option is **presence of 1 OH group and 2 P-H bonds**.

---