📘 Chapter 2 – Exploring Substances: Acidic, Basic, Neutral

🔹 Part 2: Indicators (Q26–Q50)

Q26. Which of the following is a natural indicator?

A) Phenolphthalein
B) Methyl orange
C) Litmus
D) All of these

✅ Answer: C) Litmus

Explanation:

• Phenolphthalein → Synthetic indicator.
• Methyl orange → Synthetic indicator.
• Litmus → Extracted from lichens, natural indicator (Correct).
• “All of these” is wrong since only Litmus is natural here.

Q27. Litmus solution is extracted from:

A) Plants
B) Lichens
C) Leaves
D) Fungi

✅ Answer: B) Lichens

Explanation:

• Lichens produce litmus dye (Correct).
• Other options are incorrect.

Q28. Turmeric turns red in the presence of:

A) Acids
B) Bases
C) Neutral substances
D) Water

✅ Answer: B) Bases

Explanation:

• Acids → No change.
• Bases → Turns turmeric red (Correct).
• Neutral → No change.
• Water → No change.

Q29. Which indicator is colourless in neutral solutions?

A) Litmus
B) Phenolphthalein
C) Turmeric
D) Methyl orange

✅ Answer: B) Phenolphthalein

Explanation:

• Phenolphthalein → Colourless in neutral and acidic, pink in bases (Correct).
• Litmus → Has colour.
• Turmeric → Always yellow.
• Methyl orange → Has colour.

Q30. In acidic medium, methyl orange turns:

A) Red
B) Yellow
C) Blue
D) Green

✅ Answer: A) Red

Explanation:

• Acidic → Red (Correct).
• Basic → Yellow.
• Blue/Green → Not correct for this indicator.

Q31. Which of the following is NOT an indicator?

A) China rose
B) Turmeric
C) Sodium hydroxide
D) Phenolphthalein

✅ Answer: C) Sodium hydroxide

Explanation:

• Sodium hydroxide → Strong base, not an indicator (Correct).
• Others are indicators.

Q32. Which colour does litmus show in a basic solution?

A) Red
B) Blue
C) Green
D) Yellow

✅ Answer: B) Blue

Q33. China rose indicator turns basic solution:

A) Red
B) Green
C) Pink
D) Colourless

✅ Answer: B) Green

Explanation:

• Acidic → Pink/red.
• Basic → Green (Correct).

Q34. Which of these indicators can be prepared at home?

A) Phenolphthalein
B) Turmeric
C) Methyl orange
D) None

✅ Answer: B) Turmeric

Explanation:
Turmeric is a common kitchen material that works as an indicator (Correct).

Q35. Onion juice is used as:

A) Synthetic indicator
B) Natural indicator
C) Neutralisation agent
D) Strong base

✅ Answer: B) Natural indicator

Explanation:
Onion smell changes in the presence of acids/bases, so it is a natural indicator (Correct).

Q36. Phenolphthalein shows which colour in a basic solution?

A) Red
B) Colourless
C) Pink
D) Yellow

✅ Answer: C) Pink

Explanation:

• Colourless in acidic/neutral.
• Pink in basic (Correct).

Q37. What colour does turmeric indicator show in an acidic solution?

A) Red
B) Yellow
C) Blue
D) Green

✅ Answer: B) Yellow

Explanation:

• Acidic → Yellow (Correct).
• Bases → Red.

Q38. Which natural indicator changes smell in acidic/basic medium?

A) Turmeric
B) Litmus
C) Onion
D) China rose

✅ Answer: C) Onion

Explanation:
Onion smell disappears in base but not in acid (Correct).

Q39. Methyl orange is:

A) Natural indicator
B) Synthetic indicator
C) Both
D) None

✅ Answer: B) Synthetic indicator

Q40. Which indicator turns pink in acidic solution?

A) Phenolphthalein
B) Litmus
C) China rose
D) Turmeric

✅ Answer: C) China rose

Explanation:

• Acidic → Pink/red with China rose (Correct).

Q41. What is the colour of phenolphthalein in neutral medium?

A) Red
B) Colourless
C) Yellow
D) Pink

✅ Answer: B) Colourless

Q42. Which of these is not a natural indicator?

A) Turmeric
B) Onion
C) Phenolphthalein
D) Litmus

✅ Answer: C) Phenolphthalein

Q43. Which indicator is used in titration of acids and bases in labs?

A) Turmeric
B) Litmus
C) Phenolphthalein
D) Onion

✅ Answer: C) Phenolphthalein

Q44. What colour does litmus paper turn in neutral solution?

A) Red
B) Blue
C) Green
D) No change

✅ Answer: D) No change

Q45. Which indicator is colourless in acid but pink in base?

A) Litmus
B) Phenolphthalein
C) Methyl orange
D) China rose

✅ Answer: B) Phenolphthalein

Q46. Which of these can be used to test if a substance is basic?

A) Turmeric
B) Blue litmus
C) Red litmus
D) All of these

✅ Answer: D) All of these

Explanation:

• Turmeric → Turns red in bases.
• Blue litmus → Stays blue.
• Red litmus → Turns blue in bases.
  (All are valid tests.)

Q47. Onion juice loses its smell in:

A) Acidic solution
B) Basic solution
C) Neutral solution
D) Salt solution

✅ Answer: B) Basic solution

Q48. China rose indicator turns acidic solution into:

A) Green
B) Red
C) Yellow
D) Blue

✅ Answer: B) Red

Q49. Which of these is a synthetic indicator commonly used in labs?

A) Methyl orange
B) Turmeric
C) Onion
D) China rose

✅ Answer: A) Methyl orange

Q50. Which of these is NOT used as an indicator in Class 7 experiments?

A) Turmeric
B) Onion
C) Rose petals
D) Sodium chloride

✅ Answer: D) Sodium chloride

Explanation:
Salt solution does not change colour or smell, so it is not an indicator (Correct).

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Neutralisation Class 7 Science multiple choice questions, Online learning Class 7 Science MCQ practice