The incorrect statement among the following is

<p>$\mathrm{PH_3} \text{ shows lower proton affinity than } \mathrm{NH_3}.$ </p> <p><p>Ammonia (NH₃) has a more available lone pair on nitrogen than PH₃ on phosphorus due to smaller size and higher electronegativity. Thus, NH₃ is a stronger base and has a higher proton affinity than PH₃. </p></p> <p><p>This statement is correct.</p></p> <p>$$\mathrm{SO_2} \text{ can act as an oxidizing agent, but not as a reducing agent.}$$ </p> <p><p>Sulfur dioxide (SO₂) is quite versatile in redox chemistry. In many reactions, it actually behaves as a reducing agent by being oxidized (e.g., to sulfate, where sulfur goes from +4 to +6 oxidation state). While under some conditions it may act as an oxidizing agent, it is well known and widely used for its reducing properties. </p></p> <p><p>Hence, the claim that it “cannot act as a reducing agent” is incorrect.</p></p> <p>$\mathrm{NO_2} \text{ can dimerise easily.}$ </p> <p><p>Nitrogen dioxide (NO₂) is known to dimerise to form dinitrogen tetroxide (N₂O₄), especially at lower temperatures. </p></p> <p><p>This statement is correct.</p></p> <p>$\mathrm{PF_3} \text{ exists but } \mathrm{NF_5} \text{ does not.}$ </p> <p><p>Phosphorus trifluoride (PF₃) is a known stable compound. In contrast, a compound like nitrogen pentafluoride (NF₅) is not observed, largely due to the limitations of nitrogen’s size and bonding capabilities in forming such a structure. </p></p> <p><p>This statement is correct.</p></p> <p>Based on the analysis, the incorrect statement is:</p> <p>$\textbf{Option B.}$</p>