Which of the following is not formed on hydrolysis of PCl5?

The correct answer is option 4. \(PCl_3\).

When phosphorus pentachloride (PCl₅) undergoes hydrolysis, it reacts with water to form phosphoric acid (H₃PO₄), hydrogen chloride (HCl), and intermediates such as phosphorus oxychloride (POCl₃). The complete hydrolysis reaction does not produce phosphorus trichloride (PCl₃).

Hydrolysis of PCl₅:
The hydrolysis of phosphorus pentachloride can proceed in steps:

1. Initial Hydrolysis:

\(\text{PCl}_5 + \text{H}_2\text{O} \rightarrow \text{POCl}_3 + 2\text{HCl}\)

Phosphorus pentachloride reacts with water to form phosphorus oxychloride (POCl₃) and hydrogen chloride (HCl).

2. Further Hydrolysis of POCl₃:

\(\text{POCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_4 + 3\text{HCl}\)

Phosphorus oxychloride further hydrolyzes to form phosphoric acid (H₃PO₄) and more hydrogen chloride (HCl).

Overall Hydrolysis:

The overall reaction can be written as:

\(\text{PCl}_5 + 4\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_4 + 5\text{HCl} \)

Compounds Formed:

POCl₃ (Phosphorus Oxychloride): Formed as an intermediate during the initial hydrolysis step.

H₃PO₄ (Phosphoric Acid): Final product of complete hydrolysis.

HCl (Hydrogen Chloride): Produced in both steps of the hydrolysis.

Not Formed:

PCl₃ (Phosphorus Trichloride): Phosphorus trichloride is not formed during the hydrolysis of PCl₅. Instead, PCl₃ would itself undergo hydrolysis to form H₃PO₃ (phosphorous acid) and HCl.

Therefore, the compound that is not formed on the hydrolysis of PCl₅ is: PCl₃