Which of the following statements is not correct?

Catalyst is not involved in the reaction

The correct answer is option 1. Catalyst is not involved in the reaction.

Let us break down each statement and explain why some are true and one is not:

Catalyst is not involved in the reaction (Incorrect): This statement is incorrect. A catalyst participates in a chemical reaction but is not used up in the process. It lowers the activation energy of the reaction, providing an alternative pathway for the reactants to convert to products faster. The catalyst itself gets regenerated at the end of its cycle and remains available for further reactions.

The concentration of a catalyst remains constant throughout the progress of the chemical reaction (True): This statement is true. As mentioned earlier, a catalyst is not consumed in the reaction. It forms temporary bonds with the reactants, lowers the activation energy, and then gets released in its original form. This cycle continues throughout the reaction, maintaining a relatively constant concentration of the catalyst.

The mechanism of catalytic reactions may vary from reaction to reaction (True): This statement is true. Different catalysts can work through different mechanisms to achieve the same goal of speeding up a reaction. The specific mechanism depends on the catalyst, the reactants involved, and the nature of the reaction itself.

NO acts as a homogenous catalyst in the oxidation of \(SO_2\) to \(SO_3\) (True): This statement is a valid example of a homogenous catalyst. Homogenous catalysts exist in the same phase (usually gas or liquid) as the reactants. In this case, NO participates in the gas phase along with \(SO_2\) and \(O_2\), accelerating the conversion of \(SO_2\) to \(SO_3\).

Here's an analogy to understand how a catalyst works: Imagine climbing a mountain. The normal path (uncatalyzed reaction) is steep and takes a long time. A catalyst acts like a guide who shows you a hidden path with a lower elevation (lower activation energy). This path is easier to climb (faster reaction), and the guide (catalyst) is available to help others take the same path after you reach the top (reaction completion).