Changes Around Us Physical and Chemical Class 7 MCQ
hardChanges Around Us Physical and Chemical Class 7 MCQ
Changes Around Us Physical and Chemical Class 7 MCQ
Question 1.
Which of the following is a chemical change?
(a) Melting of ice
(b) Burning of wood
(c) Chopping vegetables
(d) Boiling water
Answer:
(b) Burning of wood
Question 2.
Rusting of iron is an example of:
(a) Physical change
(b) Chemical change
(c) Both physical and chemical change
(d) Natural change
Answer:
(b) Chemical change
Question 3.
Which of the following processes involves a physical change?
(a) Baking a cake
(b) Dissolving sugar in water
(c) Burning paper
(d) Making an egg omelette
Answer:
(b) Dissolving sugar in water
Question 4.
The process of making compost from vegetable peels is:
(a) A physical change
(b) A chemical change
(c) Both physical and chemical change
(d) None of the above
Answer:
(b) A chemical change
Question 5.
What is produced when magnesium burns in air?
(a) Magnesium hydroxide
(b) Magnesium oxide
(c) Magnesium chloride
(d) Magnesium sulfate
Answer:
(b) Magnesium oxide
Question 6.
Which of the following is NOT a characteristic of a physical change?
(a) No new substance is formed
(b) The state of the substance may change
(c) A substance with different properties is formed
(d) The substance undergoes a physical reaction
Answer:
(c) A substance with different properties is formed
Question 7.
Which of the following is a reversible change?
(a) Burning of paper
(b) Melting of ice
(c) Rusting of iron
(d) Baking bread
Answer:
(b) Melting of ice
Question 8.
The process of curdling milk is an example of:
(a) Physical change
(b) Chemical change
(c) Both physical and chemical change
(d) Neither a physical nor a chemical change
Answer:
(b) Chemical change
Question 9.
Which of the following changes is an example of combustion?
(a) Melting of wax
(b) Burning of coal
(c) Freezing of water
(d) Dissolving salt in water
Answer:
(b) Burning of coal
Question 10.
The change of water to steam is:
(a) A chemical change
(b) A physical change
(c) Both physical and chemical change
(d) None of the above
Answer:
(b) A physical change
Case Study
I. Changes Around Us:
Changes occur all around us, and they can be categorized into physical and chemical changes. Physical changes involve alterations in appearance or state without forming new substances, such as melting ice or boiling water. In contrast, chemical changes result in the formation of new substances, like rusting iron or burning magnesium.
Question 1.
Which of the following is an example of a physical change?
(a) Burning a piece of paper
(b) Melting an ice cube
(c) Rusting of iron
(d) Cooking an egg
Answer:
(b) Melting an ice cube
Explanation: Melting ice involves a change in state from solid to liquid, but no new substance is formed. The chemical composition (H2O) remains the same, so it is a physical change.
Question 2.
What is a key characteristic of a chemical change?
(a) The substance changes its shape
(b) The substance changes its temperature
(c) A new substance is formed
(d) The substance changes its size
Answer:
(c) A new substance is formed
Explanation: In a chemical change, the original substances are transformed into one or more new substances with different properties, such as when iron rusts or magnesium burns.
Question 3.
Physical changes involve alterations in ............ or state without forming new substances.
Answer:
appearance
Explanation: Physical changes may change the appearance, shape, or state of a substance, but the chemical composition remains unchanged.
Question 4.
Chemical changes result in the formation of ............ substances.
Answer:
new
Explanation: Chemical changes always produce new substances with properties different from the original substances.
Question 5.
Boiling water is a chemical change because it forms a new substance. (True/False)
Answer: False
Explanation: Boiling water is a physical change. It only changes the state of water from liquid to gas (steam), but the chemical composition (H2O) remains the same.
II. The Role of Oxygen in Combustion:
To investigate the necessity of oxygen in combustion, an experiment with candles can be conducted. When one candle is covered with a glass tumbler, it extinguishes due to the lack of oxygen. This illustrates that oxygen is essential for combustion, reinforcing the concept that chemical reactions often depend on specific conditions and reactants.
Question 1.
What happens to a candle flame when it is covered with a glass tumbler?
Answer:
The candle flame goes out (is extinguished).
Question 2.
Which component of air is essential for combustion?
Answer:
Oxygen.
Question 3.
Why does the candle flame extinguish when covered with a glass tumbler,and what does this demonstrate about combustion?
Answer:
The candle flame extinguishes because the supply of oxygen is cut off; this demonstrates that oxygen is necessary for combustion to occur.