`H_(3)PO_(3)overset(Delta)toH_(3)PO_(4)+PH_(3)uarr`

Options

A. For disproportionation reaction.
B. For comproportionation reaction.
C. For either intermolecular redox reaction or displacement reaction
D. For either thermal combination redox reaction or thermal decomposition redox reaction.

Answer

To solve the question regarding the reaction of phosphorous acid (H₃PO₃) decomposing into phosphoric acid (H₃PO₄) and phosphine (PH₃), we will analyze the oxidation states of phosphorus in each compound and determine the type of reaction taking place.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
The reaction given is:
\[ \text{H}_3\text{PO}_3 \xrightarrow{\Delta} \text{H}_3\text{PO}_4 + \text{PH}_3 \]
Here, H₃PO₃ is the reactant, and H₃PO₄ and PH₃ are the products.

2. **Determine the Oxidation States**:
- For H₃PO₃:
\[ \text{Let the oxidation state of P be } x. \]
The equation for the oxidation state is:
\[ 3(1) + x + 3(-2) = 0 \implies 3 + x - 6 = 0 \implies x = +3 \]
- For H₃PO₄:
\[ \text{Let the oxidation state of P be } y. \]
The equation for the oxidation state is:
\[ 3(1) + y + 4(-2) = 0 \implies 3 + y - 8 = 0 \implies y = +5 \]
- For PH₃:
\[ \text{Let the oxidation state of P be } z. \]
The equation for the oxidation state is:
\[ 3(-1) + z = 0 \implies -3 + z = 0 \implies z = -3 \]

3. **Analyze the Changes in Oxidation States**:
- In H₃PO₃, phosphorus is in the +3 oxidation state.
- In H₃PO₄, phosphorus is in the +5 oxidation state (oxidation).
- In PH₃, phosphorus is in the -3 oxidation state (reduction).

4. **Identify the Type of Reaction**:
- Since phosphorus in H₃PO₃ is both oxidized (to +5 in H₃PO₄) and reduced (to -3 in PH₃), this is a **disproportionation reaction**.
- A disproportionation reaction is characterized by a single species undergoing both oxidation and reduction.

5. **Conclusion**:
The reaction is a **disproportionation reaction** and can also be classified as a **thermal decomposition reaction** because it involves the breakdown of a single reactant into two products upon heating.