Which of the following statement is not true?

Question

Accepted Answer

Explanation:

1. **Option 3: Depositing a layer of iron on zinc is called galvanization.**  
   This statement is not true. Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. The statement incorrectly suggests that iron is deposited on zinc, whereas it is actually zinc that is deposited on iron or steel. Therefore, this option is the correct answer as it is factually incorrect.

2. **Option 1: When a candle burns, both physical and chemical changes take place.**  
   This statement is true. When a candle burns, the wax melts (a physical change) and then vaporizes and reacts with oxygen in the air to produce carbon dioxide and water (a chemical change). Thus, both physical and chemical changes occur during the burning of a candle.

3. **Option 2: Anaerobic bacteria digest animal waste and produce biogas.**  
   This statement is true. Anaerobic bacteria break down organic matter, such as animal waste, in the absence of oxygen to produce biogas, which primarily consists of methane and carbon dioxide. This process is widely used in biogas production systems.

4. **Option 4: Stretching of rubber band is a physical change.**  
   This statement is true. Stretching a rubber band involves changing its shape and length, which is a physical change. The rubber band returns to its original shape when the force is removed, indicating that no chemical change has occurred.

In conclusion, Option 3 is the correct answer because it inaccurately describes the process of galvanization, whereas the other options accurately describe the processes they refer to.