Assertion: In `H_(3)PO_(3)` basicity of the oxy acid is two.
Reason: One H-atom is non-ionizable in more stable tautomeric form of `H_(3)PO_(3)`.

Options

A. If both (A) and (R) are true and (R) is the correct explanation of (A)
B. if both (A) and (R) are true but (R) is not correct explanation of (A)
C. If (A) is true but (R) is false
D. If (A) is false but (R) is false

Explanation

To solve the question, we need to analyze both the assertion and the reason provided regarding the compound \( H_3PO_3 \) (phosphorous acid).

### Step-by-Step Solution:

1. **Understanding Basicity**:
- Basicity of an acid refers to the number of hydrogen ions (H⁺) that can be replaced by a base. For oxyacids, this is determined by the number of ionizable hydrogen atoms.

2. **Structure of \( H_3PO_3 \)**:
- The structure of \( H_3PO_3 \) can be represented as:
\[ \text{H}_3\text{PO}_3: \text{H} - \text{O} - \text{P}(\text{OH})_2 \]
- In this structure, there are three hydrogen atoms, but not all are ionizable.

3. **Tautomerization**:
- \( H_3PO_3 \) can undergo tautomerization to form a more stable structure. The tautomerization involves the conversion of one of the hydroxyl groups into a double bond with phosphorus, resulting in:
\[ \text{H}_2\text{P}=\text{O} - \text{OH} \]
- In this tautomeric form, one of the hydrogen atoms is directly attached to phosphorus, making it non-ionizable.

4. **Identifying Ionizable Hydrogens**:
- After tautomerization, we can see that:
- Two hydrogen atoms are attached to hydroxyl groups (OH) and can be ionized.
- One hydrogen atom is attached directly to phosphorus and cannot be ionized.

5. **Conclusion on Basicity**:
- Since only two hydrogen atoms can be released as H⁺ ions, the basicity of \( H_3PO_3 \) is 2.

6. **Assertion and Reason Evaluation**:
- **Assertion**: The basicity of \( H_3PO_3 \) is 2. (True)
- **Reason**: One hydrogen atom is non-ionizable in the more stable tautomeric form of \( H_3PO_3 \). (True)
- Since both the assertion and reason are true, and the reason correctly explains the assertion, we conclude that the correct option is that both assertion and reason are true and the reason is the correct explanation of the assertion.

### Final Answer:
The correct option is **Option 1**: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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