Class 7 chemistry MCQs with answers are provided here for chapter 6 Physical and Chemical Changes. These MCQs are based on the CBSE board curriculum and correspond to the most recent Class 7 chemistry syllabus. By practising these Class 7 multiple choice questions, students will be able to quickly review all of the ideas covered in the chapter and prepare for the Class 7 annual examinations as well as other competitive exams.
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Class 7 Physical and Chemical Changes MCQs
Q-1: Which of the following describes the process of depositing a zinc layer on iron?
a) Galvanisation
b) Crystallisation
c) Rusting
d) None of the above
Answer: a) Galvanisation
Explanation: Galvanisation refers to the process of depositing a layer of zinc on iron in order to prevent it from rusting.
Q-2: Which of the following are stainless steel constituents?
a) Iron, Carbon, Nickel, Chromium
b) Iron, Nickel, Manganese
c) Iron, Nickel, Carbon, Manganese, Chromium
d) Carbon, Iron, Nickel
Answer: c) Iron, Nickel, Carbon, Manganese, Chromium
Explanation: Stainless steel is created by combining iron, carbon, and metals such as chromium, nickel, and manganese.
Q-3: Which of the following is not a chemical change characteristic?
a) Change in colour
b) Change in state
c) Production of sound
d) Change in smell
Answer: b) Change in state
Explanation: A change in which one or more new substances are formed is called a chemical change. Aside from new products, a chemical change may result in the following:
- Heat, light, or any other form of radiation (for example, ultraviolet) may be given either off or absorbed.
- Sound may be produced.
- A change in smell may occur.
- A new odour may be released.
- A colour change may take place.
Thus, a change in physical state is not a chemical change characteristic.
Q-4: What kind of change occurs when the tip of the blade is placed on a gas stove?
a) Chemical change
b) Physical change
c) No change
d) Irreversible change
Answer: b) Physical change
Explanation: When the tip of the blade is placed on a gas stove, it turns black. A physical change occurs when a substance undergoes a change in its physical properties, such as shape, colour, size, or state. Since the change in colour is occurring, it’s a physical change.
Q-5: When magnesium is burned in the air, it produces powdery ash that, when dissolved in water, yields an aqueous solution. How will you categorise the aqueous solution?
a) Acidic
b) Neutral
c) Basic
d) Can’t be predicted
Answer: c) Basic
Explanation: When the ash is dissolved in water, it forms an aqueous solution of magnesium hydroxide. When the aqueous solution was tested with red litmus paper, it turned blue, indicating that it was a basic solution.
Q-6: Which of the following does not represent a chemical change?
a) Burning of leaves
b) Fermentation of grapes
c) Turning brown of freshly cut banana
d) Freezing of water
Answer: d) Freezing of water
Explanation: When water freezes, its state changes from liquid to solid. Because the physical state of water is changing, it is considered as a physical change.
Q-7: What kind of change is the explosion of fireworks?
a) Physical change
b) Chemical change
c) Not a change
d) Reversible change
Answer: b) Chemical change
Explanation: A firework explosion is a chemical change. Such an explosion produces heat, light, sound and unpleasant gases, which are characteristics of a chemical change.
Q-8: When food spoils, it emits a foul odour as a result of a chemical change. What is the name given to this process?
a) Rusting
b) Rancidity
c) Crystallisation
d) Corrosion
Answer: b) Rancidity
Explanation: Food contains fats which, when exposed to air, get oxidised and result in the formation of products which have bad taste and smell. This oxidation of food is known as rancidity.
Q-9: Which of the following is not a required condition for rusting to occur?
a) Presence of oxygen
b) Presence of CO2
c) Presence of water vapour
d) Presence of water
Answer: b) Presence of CO2
Explanation: For rusting, the presence of both oxygen and water (or water vapour) is essential.
Q-10: Which of the following is a physical change?
a) Cutting a log of wood into pieces
b) Ripening of a fruit
c) Formation of manure from leaves
d) Formation of salt from acid and base
Answer: a) Cutting a log of wood into pieces
Q-11: If you leave a piece of iron out in the open for a while, it will develop a brownish film. What is the name of this brown substance?
a) Dust
b) Rust
c) Both a) and b)
d) Brown sand
Answer: b) Rust
Q-12: Which of the following chemical is responsible for making lime water milky?
a) Calcium carbonate
b) Calcium hydroxide
c) Calcium chloride
d) Calcium oxide
Answer:a) Calcium carbonate
Explanation: Calcium carbonate is formed when carbon dioxide is passed through lime water, making the lime water milky.
Q-13: Which of the following is another name for copper sulphate?
a) Green vitriol
b) Blue vitriol
c) Neela thotha
d) Both b) and c)
Answer: d) Both b) and c)
Q-14: When a used shaving blade is dropped into a blue-coloured copper sulphate solution, a brown colour deposit forms on _____, and the solution turns green due to the formation of ________.
a) Iron, ferrous sulphate
b) Copper, ferrous sulphate
c) Copper, copper sulphate
d) Iron, copper
Answer: a) Iron, ferrous sulphate
Explanation: When a shaving blade is placed in a copper sulphate solution, the colour changes from blue to green due to the formation of iron sulphate, a new substance. Copper, another new substance, is the brown deposit on the iron nail.
The reaction can be written as:
Copper sulphate solution (blue) + Iron → Iron sulphate solution (green) + Copper (brown deposit)
Q-15: Which of the following is a characteristic of burning?
a) It is accompanied by the production of heat.
b) O2 is required for burning.
c) Burning is a chemical change.
d) All of the above
Answer: d) All of the above
Explanation: Burning requires O2 and is always accompanied by the production of heat. It is considered a chemical change because new products are formed (CO2, heat etc.).
Q-16: Which of the following properties is not changed in a physical change?
a) Colour
b) Size
c) Shape
d) Composition
Answer: d) Composition
Explanation: In a physical change, only the physical properties are changed, like colour, size, shape and state; composition of the reactants retained in the product formed.
Q-17: Which of the following gas absorbs harmful ultraviolet radiations coming from the sun?
a) O2
b) O3
c) CO2
d) N2
Answer: b) O3
Explanation: The ozone layer shields us from the sun’s harmful ultraviolet radiation. Ozone(O3) absorbs this radiation and converts it to oxygen. If ozone did not absorb ultraviolet radiation, it would reach the earth’s surface and endanger us and other living things. Ozone acts as natural protection against this radiation.
Q-18: Which of the following is to blame for ships rusting despite being painted?
a) Impurities present in seawater
b) Marine life in seawater
c) Salts present in seawater
d) All of the above
Answer: c) Salts present in seawater
Explanation: Ships are made of iron, and a portion of them is submerged.
Water drops continue to cling to the ship’s outer surface above water as well. Furthermore, seawater contains a high concentration of salts. The salt water accelerates the rust formation process. As a result, despite being painted, ships sustain significant rust damage.
Q-19: By dissolving sugar in hot water, Rita’s mother created a concentrated sugar syrup. Sugar crystals separated during cooling. This denotes a:
(a) Physical change that is reversible
(b) Chemical change that is reversible
(c) Irreversible physical change
(d) Irreversible chemical change
Answer: a) Physical change that is reversible
Explanation: Because Rita’s mother was able to recover sugar crystals from sugar syrup after cooling, the change is reversible. And it is a physical change, as there is no chemical reaction when sugar is dissolved in hot water.
Q-20: Test tubes P and Q contain equal amounts of aqueous hydrochloric acid. On adding magnesium to test tube P and sodium carbonate to test tube Q, which of the following observations will be observed?
i) The gas evolved in both the test tubes will extinguish a burning splinter.
ii) The gas evolved in a test tube Q will extinguish a burning splinter with a pop sound.
iii) The gas evolved in test tube P will turn lime water milky.
iv) The gases evolved in test tubes P and Q are H2 and CO2, respectively.
a) i), ii) and iii)
b) i) and iv)
c) i), iii) and iv)
d) iii) and iv)
Answer: b) i) and iv)
Explanation: The reaction taking place in test tube P is:
Mg + 2HCl → MgCl2 + H2
The reaction taking place in test tube Q is:
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
We can clearly see from the above reactions that H2 gas evolved in test tube P and CO2 evolved in test tube Q. Both gases which evolved have the ability to extinguish a burning splinter, with the only difference being that the H2 gas does so with a pop sound.
Read Also:
- Difference between Physical and Chemical Change
- Chemical and Physical Change Examples
- Chemical and Physical Change
- What Are Physical and Chemical Changes?
- Chapter 6 Physical and Chemical Changes Worksheet-Set-1
- Chapter 6 Physical and Chemical Changes Worksheet-Set-2
- Chapter 6 Physical and Chemical Changes Worksheet-Set-3
- Chemistry Concept Questions and Answers
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