Question

A change is said to be a chemical change when-

• A. new substances are formed
• B. energy changes occur
• C. the change cannot be easily reversed
• D. all statements are correct

Answer 1

The correct option is D

all statements are correct

Explanation of the correct answer (Option D):

New substances are formed:

1. A chemical change is a type of chemical reaction in which new substances are formed when atoms of two or more than two molecules react together.
2. The formation of new substances can be characterized by color change, odor, bubble formation, formation of precipitates, the evolution of gas, etc.

Energy changes occur:

1. In a chemical change, the molecules of the reactants need energy to break the bond and form new substances.
2. Energy is either released or gained during a chemical change.
3. Change in heat, electricity, and light, all are forms of energy that occur during a chemical change.

The change cannot be easily reversed:

1. The changes that occur during a chemical change or a chemical reaction cannot be reversed because of the different chemical compositions and properties of the products formed as compared to the reactants.
2. Example: Souring of milk is a chemical change in which the lactose in milk is converted into lactic acid by the action of bacteria. This change cannot be reversed.

Hence, the correct option is D (all statements are correct)