CBSE Class 7 Science Chapter 02 Exploring Substances Acidic, Basic, And Neutral MCQs Set 03

Practice MCQs for Class 7 Science Chapter 02 Exploring Substances Acidic, Basic, And Neutral

Access targeted multiple-choice questions for Chapter 02 Exploring Substances Acidic, Basic, And Neutral designed to align with the latest CBSE academic syllabus for Class 7 Science. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

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Question: According to the acids chart in Fig. 2.4, which acid is mainly associated with oranges?
A. Citric acid
B. Tartaric acid
C. Oxalic acid
D. Ascorbic acid
Show Answer & Explanation

Answer: (A) Citric acid

Explanation:
The chart pairs citrus fruits like oranges with citric acid, distinguishing it from tartaric acid (linked to mango) and the combined ascorbic-citric acid pairing shown for amla.

Question: The food-acids chart links tomatoes to which pair of acids?
A. Citric acid and oxalic acid
B. Tartaric acid alone
C. Ascorbic acid and citric acid
D. Formic acid and citric acid
Show Answer & Explanation

Answer: (A) Citric acid and oxalic acid

Explanation:
Tomatoes are shown with a two-acid combination, citric and oxalic acid, unlike mango which contains only tartaric acid.

Question: A solution turns red litmus paper blue, showing it is basic. What would happen if vinegar were added to it in large amounts?
A. The litmus colour would revert to red as the acid takes over
B. There would be no visible change at all
C. The solution would become even more basic
D. The mixture would turn into a solid salt instantly
Show Answer & Explanation

Answer: (A) The litmus colour would revert to red as the acid takes over

Explanation:
Vinegar is acidic, so pouring it in excess overwhelms the base and neutralises it past the balance point, pushing the litmus colour back toward red.

Question: In Activity 2.7, once lime water turned the acidic solution's colour from red to blue, a student added one more drop of lemon juice. What would most likely happen next?
A. The colour would shift back toward red
B. The colour would stay permanently blue
C. The liquid would immediately boil
D. The colour would turn green
Show Answer & Explanation

Answer: (A) The colour would shift back toward red

Explanation:
Adding fresh acid after the base had neutralised the mixture tips the balance toward acidity again, so the blue colour would reverse toward red.

Question: In Activity 2.3, why is pouring hot water into the crushed rose petals meant to be done only under adult supervision?
A. To avoid accidental burns or scalds while handling hot water
B. Because rose petals ignite when heated
C. Because the glass tumbler dissolves in hot water
D. Because darkness is needed for the extract to form
Show Answer & Explanation

Answer: (A) To avoid accidental burns or scalds while handling hot water

Explanation:
Handling hot water always carries a scalding risk for young learners, which is why the activity flags adult supervision at that particular step.

Question: The note on lichens mentions that they grow well on rocks and trees under which conditions?
A. Places with plenty of rainfall and clean air
B. Dry, dusty desert regions
C. Areas heavily polluted by factories
D. Dark caves with no sunlight
Show Answer & Explanation

Answer: (A) Places with plenty of rainfall and clean air

Explanation:
Since lichens are sensitive organisms formed by a fungus-alga partnership, the chapter notes they thrive where rainfall is abundant and the air is unpolluted.

Question: A boy noticed that a turmeric curry stain on his shirt changed colour after he applied soap to wash it. What best explains this?
A. Soap is basic, and it alters turmeric's colour on contact
B. Soap is acidic and simply bleaches out the stain
C. Turmeric is a synthetic dye that fades in water
D. Sunlight, not soap, caused the colour change
Show Answer & Explanation

Answer: (A) Soap is basic, and it alters turmeric's colour on contact

Explanation:
Turmeric acts as a natural indicator that turns reddish when it meets a basic substance, and soap solutions are basic in nature — which is exactly why the stain's colour shifted.

Question: The 'Fascinating Facts' box describes turmeric as the golden spice belonging to which plant family?
A. Ginger family
B. Citrus family
C. Rose family
D. Legume family
Show Answer & Explanation

Answer: (A) Ginger family

Explanation:
Turmeric is described as a relative of ginger, grown widely in India and valued both as a spice and in Ayurvedic remedies.

Question: Besides litmus, red rose extract, and turmeric, which other materials are suggested for experimenting with as natural indicators?
A. Beetroot, purple cabbage, and hibiscus flowers
B. Baking soda and washing powder
C. Tap water and common salt
D. Lime and calcium oxide
Show Answer & Explanation

Answer: (A) Beetroot, purple cabbage, and hibiscus flowers

Explanation:
The text encourages readers to try extracts from beetroot, purple cabbage, jamun, and red hibiscus, since these too can behave as acid-base indicators.

Question: Among the samples tested in Activity 2.1, which one was NOT placed in Group A along with lemon juice, amla juice, and vinegar?
A. Baking soda solution
B. Tamarind water
C. Amla juice
D. Vinegar
Show Answer & Explanation

Answer: (A) Baking soda solution

Explanation:
Baking soda solution turned red litmus paper blue, so it was sorted into the basic Group B rather than the acidic Group A.

Question: One of the practice exercises describes a solution that turns red litmus paper blue. Adding an excess of which substance would most likely flip the colour back to red?
A. Vinegar
B. Lime water
C. Baking soda solution
D. Washing powder solution
Show Answer & Explanation

Answer: (A) Vinegar

Explanation:
A solution that turns red litmus blue is basic, so only an acidic substance can cancel out that effect. Vinegar is acidic, while the other three options are all basic substances mentioned in the chapter, so they would not reverse the colour.

Question: Three unknown solutions were tested: red litmus turned blue in solution A, turmeric solution turned red in solution B, and red rose extract turned green in solution C. What can be concluded about them?
A. A is neutral while B and C are basic
B. All three are acidic
C. A and B are basic while C is acidic
D. All three are basic
Show Answer & Explanation

Answer: (D) All three are basic

Explanation:
• Red litmus turning blue means solution A is basic.
• Turmeric turning red is a reaction that only happens with basic substances, so B is basic too.
• Red rose extract turning green also signals a basic nature, making C basic as well.
Since every indicator points the same way, all three solutions must be basic.

Question: A laboratory liquid produced no change with red litmus, turned blue litmus red, and left turmeric paper unchanged. What is its nature?
A. Neutral
B. Basic
C. Acidic
D. Cannot be determined
Show Answer & Explanation

Answer: (C) Acidic

Explanation:
Turning blue litmus red while leaving red litmus unaffected is the classic sign of an acid, and the lack of change in turmeric paper fits too, since turmeric only reacts with basic substances.

Question: When grape juice was mixed with red rose extract, the mixture took on a reddish tinge. What would most likely happen if baking soda were then stirred into this mixture?
A. The mixture would become completely colourless
B. The colour would shift toward green as the base neutralises the acidic juice
C. The red colour would only get deeper and darker
D. Nothing would change since baking soda has no effect on indicators
Show Answer & Explanation

Answer: (B) The colour would shift toward green as the base neutralises the acidic juice

Explanation:
The red tinge shows the grape juice mixture is acidic, and rose extract is known to turn green in basic conditions. Adding baking soda, a base, would gradually push the mixture toward that green shade as it neutralises the acid.

Question: Even after confirming that a garden's soil is neutral, the plants continue to look unhealthy. What explanation does the chapter offer for this situation?
A. The soil may be lacking in nutrients needed for plant growth
B. The soil is secretly still acidic
C. The soil has too much lime mixed into it
D. The soil has absorbed excess baking soda
Show Answer & Explanation

Answer: (A) The soil may be lacking in nutrients needed for plant growth

Explanation:
Neutral just means the soil is neither acidic nor basic, so a plant can still struggle for other reasons — the chapter points out that nutrient deficiency in otherwise neutral soil can be the real culprit.

Question: The fruit called lime is easily confused with the substance used to make lime water. Chemically speaking, what is lime water?
A. A solution of calcium hydroxide dissolved in water
B. Juice squeezed directly from lime fruit
C. A mixture of vinegar and baking soda
D. A solution of citric acid in water
Show Answer & Explanation

Answer: (A) A solution of calcium hydroxide dissolved in water

Explanation:
Lime water is prepared by mixing calcium oxide (chuna) with water and letting it settle before filtering — the resulting liquid is a solution of calcium hydroxide, unrelated to the citrus fruit of the same name.

Question: In the olfactory indicator activity, chopped onion pieces along with cloth or paper strips were sealed in a container and left untouched overnight. Why was this waiting period necessary?
A. So the strips could soak up the onion's smell before being tested
B. So the onion pieces would dry out completely
C. So the tamarind water would not evaporate too quickly
D. So the baking soda solution could dissolve fully
Show Answer & Explanation

Answer: (A) So the strips could soak up the onion's smell before being tested

Explanation:
Leaving the strips sealed with the onion overnight lets them pick up a strong onion odour, which is essential — without that absorbed smell, there would be nothing for the acidic or basic drops to change later.

Question: Leaving aside the blank 'any other' entry, how many distinct samples were listed for testing with litmus paper in the activity table?
A. 8
B. 9
C. 11
D. 13
Show Answer & Explanation

Answer: (C) 11

Explanation:
The table lists lemon juice, soap solution, amla juice, tamarind water, vinegar, baking soda solution, lime water, tap water, washing powder solution, sugar solution, and salt solution — eleven named samples in total.

Question: After noticing that baking soda solution feels slippery, a boy exclaims that he can now test his floor cleaning liquid with an indicator. What does this reaction reveal about him?
A. He has understood that the idea of indicators applies beyond the classroom to everyday household items
B. He believes floor cleaners are always neutral in nature
C. He thinks litmus paper is the only usable indicator
D. He wants to stop using baking soda in future experiments
Show Answer & Explanation

Answer: (A) He has understood that the idea of indicators applies beyond the classroom to everyday household items

Explanation:
His comment shows he's connecting a classroom concept to real life, realising that any household liquid, not just lab samples, can be checked for its acidic or basic nature using simple indicators.

Question: The chapter briefly mentions synthetic indicators alongside natural ones like litmus. When does it say students will study these in greater detail?
A. In higher grades
B. Immediately in the next activity
C. During the science fair
D. Never, as they are outside the syllabus
Show Answer & Explanation

Answer: (A) In higher grades

Explanation:
Synthetic indicators are only introduced by name here; the chapter defers a deeper explanation of them to later years of schooling.

Question: Acharya Prafulla Chandra Ray wrote extensively on the history of chemistry in India. What was his purpose in doing so, as described in the chapter?
A. To bring recognition to the achievements of ancient Indian scientists on a global stage
B. To convince farmers to adopt chemical fertilisers
C. To promote synthetic indicators over natural extracts
D. To document the medicinal uses of turmeric
Show Answer & Explanation

Answer: (A) To bring recognition to the achievements of ancient Indian scientists on a global stage

Explanation:
Ray's historical writings were not just academic records.
• They showcased the scientific expertise of ancient India
• They aimed to place these achievements before an international audience
• This reflected his broader pride in Indian knowledge traditions

Question: Which sequence correctly describes the order of steps carried out in the activity where lemon juice and soap solution were tested using red rose extract?
A. Place rose extract in two tubes, add lemon juice to one and soap solution to the other, then observe the colour change
B. Mix lemon juice and soap solution together first, then divide into two tubes
C. Observe colour change first, then add the rose extract afterwards
D. Add soap solution to the extract, then pour in lemon juice, then add more extract
Show Answer & Explanation

Answer: (A) Place rose extract in two tubes, add lemon juice to one and soap solution to the other, then observe the colour change

Explanation:
The rose extract goes into two separate tubes first; only then are the two different samples added one at a time so their individual effects on colour can be compared side by side.

Question: In the activity asking whether Group A substances are edible and prompting students to recall their taste, what is the chapter really trying to achieve?
A. Helping students link the familiar sour taste of everyday foods to the property of being acidic
B. Testing whether students can identify synthetic indicators
C. Proving that all sour-tasting foods are unsafe to eat
D. Showing that edible items can never be acidic
Show Answer & Explanation

Answer: (A) Helping students link the familiar sour taste of everyday foods to the property of being acidic

Explanation:
By getting students to recall the sour taste of things like lemon juice and tamarind water, the activity builds an intuitive, everyday sense of what 'acidic' means rather than relying only on litmus results.

Question: Among the exploratory projects listed at the end of the chapter, which one directly involves creating something artistic using natural indicators?
A. Making a rangoli design using acidic or basic substances along with natural indicators
B. Constructing a working model of a volcano
C. Designing a poster explaining synthetic indicators
D. Writing an essay on industrial waste treatment
Show Answer & Explanation

Answer: (A) Making a rangoli design using acidic or basic substances along with natural indicators

Explanation:
One of the suggested projects invites students to combine art and science by using natural indicators to create colourful rangoli patterns.

Question: When a red ant bites, what acidic substance does it inject into the skin?
A. Formic acid
B. Citric acid
C. Tartaric acid
D. Oxalic acid
Show Answer & Explanation

Answer: (A) Formic acid

Explanation:
The stinging sensation from an ant bite comes from formic acid entering the skin, which is why rubbing on a mild base like moist baking soda brings relief.

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