Which of the following environmental changes is classified as a physical change?
💡 UNEB Examiner Insight & Textbook Rationale
Melting is a physical change because it is temporary, fully reversible upon cooling, and no new substance is formed.
P.5 • Topic 9 Question 2 of 8
1 Mark • UNEB Standard
Which pair of conditions is necessary for an iron hoe to rust?
💡 UNEB Examiner Insight & Textbook Rationale
Both oxygen and moisture (water) must be present together for iron to undergo rusting.
P.5 • Topic 9 Question 3 of 8
1 Mark • UNEB Standard
In the 4-test-tube experiment on rusting, what was the function of boiling the water in Test-Tube B?
💡 UNEB Examiner Insight & Textbook Rationale
Boiling water removes and expels all dissolved gases, specifically oxygen, creating an oxygen-free medium.
P.5 • Topic 9 Question 4 of 8
1 Mark • UNEB Standard
Which method is commonly used to protect food storage cans from rusting without poisoning food?
💡 UNEB Examiner Insight & Textbook Rationale
Tin plating is ideal for food cans because tin does not rust and is non-poisonous to human health.
P.5 • Topic 9 Question 5 of 8
1 Mark • UNEB Standard
A dry bean seed absorbs water, germinates, and grows into a tall bean plant. Why is this called a biological change?
💡 UNEB Examiner Insight & Textbook Rationale
Biological changes occur exclusively within living things and cannot be reversed back to the initial state.
P.5 • Topic 9 Question 6 of 8
1 Mark • UNEB Standard
What happens when cold water is poured over a sealed metallic can filled with hot steam?
💡 UNEB Examiner Insight & Textbook Rationale
Condensation of steam rapidly reduces internal pressure, creating a partial vacuum. The higher outside atmospheric air pressure crushes the can inward.
P.5 • Topic 9 Question 7 of 8
1 Mark • UNEB Standard
Which of the following is a constructive (good) people-made environmental change?
💡 UNEB Examiner Insight & Textbook Rationale
Afforestation (planting trees where none existed) and mulching bare soil are constructive activities that protect soil and conserve moisture.
P.5 • Topic 9 Question 8 of 8
1 Mark • UNEB Standard
Why does an iron nail rust fastest when placed in salty water?
💡 UNEB Examiner Insight & Textbook Rationale
Salt ions act as powerful electrolytes that speed up the transfer of electrons during the oxidation of iron, accelerating rusting.
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