\(4H_3PO_3 \longrightarrow 3 H_3PO_4 + PH_3\)

What type of chemical reaction is exhibited by the above chemical reaction?

Disproportionation

The correct answer is option 3. Disproportionation.

The reaction given is:

\(4H_3PO_3 \longrightarrow 3H_3PO_4 + PH_3\)

To understand what type of reaction this is, we need to look at the oxidation states of phosphorus in the reactants and products.

Phosphorous Acid (\(H_3PO_3\))

In \(H_3PO_3\), phosphorus has an oxidation state of +3. Hydrogen (+1 each) and Oxygen (-2 each) balance to give phosphorus +3.

\(3(\text{+1}) + x + 3(-2) = 0 \\3 + x - 6 = 0 \\x = +3 \)

Phosphoric Acid (\(H_3PO_4\)

In \(H_3PO_4\), phosphorus has an oxidation state of +5.

\(3(\text{+1}) + x + 4(-2) = 0 \\ 3 + x - 8 = 0 \\ x = +5\)

Phosphine (\(PH_3\))

In \(PH_3\), phosphorus has an oxidation state of -3.

\(x + 3(-1) = 0 \\ x - 3 = 0 \\ x = -3\)

Analysis of the Reaction

In the given reaction:

\(4H_3PO_3 \longrightarrow 3H_3PO_4 + PH_3\)

Phosphorus in \(H_3PO_3\) is oxidized to \(H_3PO_4\) (from +3 to +5).

Phosphorus in \(H_3PO_3\) is reduced to \(PH_3\) (from +3 to -3)

Disproportionation Reaction

A disproportionation reaction is a type of redox reaction where: A single element undergoes both oxidation and reduction. In this reaction, phosphorus is being simultaneously oxidized (from +3 to +5) and reduced (from +3 to -3).

Summary

Oxidation: Phosphorus in \(H_3PO_3\) is converted to \(H_3PO_4\), where it has a higher oxidation state (+5).

Reduction: Phosphorus in \(H_3PO_3\) is converted to \(PH_3\), where it has a lower oxidation state (-3).

Thus, the reaction is characterized by the element phosphorus undergoing both oxidation and reduction, making it a disproportionation reaction.