Science quiz page testing students' understanding of the differences between physical and chemical changes through true/false statements and examples.

Q.4: True or False

Let's analyze each statement one by one:

#### 1) A change in size or shape is physical change.
- True: A physical change involves a change in the form or appearance of a substance without altering its chemical composition. Examples include melting, freezing, cutting, or bending. These changes do not produce new substances.

#### 2) A chemical substance means new substance with new properties was formed.
- True: A chemical substance is formed when a chemical reaction occurs, resulting in the formation of new substances with different properties from the original reactants. This is the defining characteristic of a chemical change.

#### 3) Chemical change is when water freezes.
- False: Freezing is a physical change, not a chemical change. When water freezes, it changes from a liquid to a solid state, but the chemical composition (H₂O) remains the same. No new substance is formed.

#### 4) When milk turns sour, it is a physical change as change in odour do not indicate chemical change.
- False: When milk turns sour, it undergoes a chemical change. The bacteria in the milk break down lactose into lactic acid, which alters the chemical composition and produces new substances. The change in odor is a result of these new substances being formed, indicating a chemical change.

Final Answers for Q.4:

1. True
2. True
3. False
4. False

---

Q.5: Give examples of:

#### 1. Chemical Change
A chemical change involves the formation of new substances with different properties. Here are two examples:

- a) Rusting of iron: When iron reacts with oxygen and moisture in the air, it forms rust (iron oxide). The chemical formula for this reaction is:
\[
4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3
\]
Rust is a new substance with different properties from iron.

- b) Burning of wood: When wood burns, it reacts with oxygen in the air to produce carbon dioxide and water vapor. The chemical formula for this reaction is:
\[
\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}
\]
Carbon dioxide and water are new substances formed during this process.

#### 2. Physical Change
A physical change involves a change in the form or appearance of a substance without altering its chemical composition. Here are two examples:

- a) Melting of ice: When ice melts, it changes from a solid to a liquid state, but the chemical composition (H₂O) remains unchanged.

- b) Cutting a piece of paper: When you cut a piece of paper, its size and shape change, but the chemical composition of the paper remains the same.

Final Answers for Q.5:

1. Chemical Change:
- a) Rusting of iron
- b) Burning of wood

2. Physical Change:
- a) Melting of ice
- b) Cutting a piece of paper

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Boxed Final Answers:

Q.4:
1. True
2. True
3. False
4. False

Q.5:
1. Chemical Change:
- a) Rusting of iron
- b) Burning of wood

2. Physical Change:
- a) Melting of ice
- b) Cutting a piece of paper

Final Answer:
\boxed{
\begin{array}{l}
\text{Q.4:} \\
1. \text{True} \\
2. \text{True} \\
3. \text{False} \\
4. \text{False} \\
\\
\text{Q.5:} \\
1. \text{Chemical Change:} \\
\text{a) Rusting of iron} \\
\text{b) Burning of wood} \\
2. \text{Physical Change:} \\
\text{a) Melting of ice} \\
\text{b) Cutting a piece of paper} \\
\end{array}
}