116 practice questions on Exploring Substances: Acidic, Basic, and Neutral, a chapter in the NCERT Class 7 Science textbook, organised into 3 topics. Every question includes a written explanation. Pick a topic below, or try the samples first.
Turmeric changes from yellow to red only with a base, which is the whole point of using it as an indicator. An acid leaves turmeric yellow, so the acidic solution is wrong. A neutral solution and distilled water also leave it yellow, so neither of those produces a change.
Q2
medium
Lime water, milk of magnesia and a solution of washing soda are all basic. All three would therefore
Aleave both litmus papers unchanged
Bturn blue litmus paper red
Ctaste sour
Dturn red litmus paper blue
Show answer and explanation
Correct answer: D - turn red litmus paper blue
Bases turn red litmus blue, so all three would give that change. Turning blue litmus red is what an acid does. Leaving both papers unchanged is the behaviour of a neutral substance. A sour taste belongs to acids, not to these three.
Q3
medium
A few drops of china rose extract are added to a glass of lime water. What colour is expected?
AGreen
BYellow
COrange
DMagenta
Show answer and explanation
Correct answer: A - Green
Lime water is basic, and china rose extract turns green in a base. Magenta would appear only if the liquid were acidic, which lime water is not. Yellow and orange are not colours this indicator gives with either an acid or a base.
Q4
medium
Statement I: A neutral solution changes the colour of neither litmus paper. Statement II: A neutral solution turns turmeric paper red. Which of these is correct?
AOnly Statement II is correct
BOnly Statement I is correct
CBoth statements are correct
DNeither statement is correct
Show answer and explanation
Correct answer: B - Only Statement I is correct
Statement I is correct, since leaving both litmus papers unchanged is exactly how a neutral solution behaves. Statement II is wrong, because turmeric turns red only with a base and stays yellow in a neutral solution. So only the first statement stands.
Q5
easy
Litmus, the best known laboratory indicator, is obtained from
Aturmeric roots
Btea leaves
Clichens
Drose petals
Show answer and explanation
Correct answer: C - lichens
Litmus is a dye taken from lichens, which are small growths found on rocks and tree bark. Rose petals give a different natural indicator, and turmeric roots give the yellow turmeric indicator. Tea leaves are not used to prepare litmus at all.
Q6
medium
Why is it dangerous to taste an unknown liquid in order to find out whether it is acidic?
AIt may make the liquid useless for the rest of the experiment
BIt may be corrosive or poisonous and can injure the mouth and throat
CIt may change colour once it is inside the mouth
DIt may spoil the taste of the next meal
Show answer and explanation
Correct answer: B - It may be corrosive or poisonous and can injure the mouth and throat
Laboratory acids and bases can burn the soft lining of the mouth and throat, and some substances are poisonous, so tasting risks serious injury. Spoiling a meal or wasting a sample are trivial worries beside that. Whether the liquid changes colour in the mouth is not the danger, and it would not be safe even if it did not.
Practice the full Exploring Substances: Acidic, Basic, and Neutral bank free
All 116 questions with timed practice, instant scoring, and explanations. Free forever.