Which of the following is not a chemical reaction?

Explanation

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. In a chemical reaction, the bonds between atoms are broken and new bonds are formed, resulting in the production of new substances with different properties.

Option A: Burning of bush is a chemical reaction called combustion. During combustion, organic matter (like plants) reacts with oxygen in the air to produce carbon dioxide, water, and heat energy. So, this is a chemical reaction.

Option B: Rusting of iron is also a chemical reaction called oxidation. In this process, iron reacts with oxygen and water in the air to form hydrated iron(III) oxide, which is commonly known as rust. This is a chemical reaction as well.

Option C: Decay of bitter leaves involves the decomposition of organic matter by microorganisms. This process involves various chemical reactions that break down complex organic molecules into simpler substances such as carbon dioxide, water, and nutrients. Therefore, the decay of bitter leaves is a result of chemical reactions.

Option D: Dissolution of potassium hydroxide pellets is the correct answer because it is not a chemical reaction. Dissolution is a physical process where a solute (in this case, potassium hydroxide pellets) is dissolved in a solvent (usually water) to form a solution. In this process, no new substances are formed, and the bonds between the atoms in the solute are not broken or changed. Instead, the solute particles are simply surrounded by solvent molecules and dispersed evenly throughout the solution.

In summary, dissolution of potassium hydroxide pellets is not a chemical reaction, while burning of bush, rusting of iron, and decay of bitter leaves are all examples of chemical reactions.