Exploring Substances: Acidic, Basic, and Neutral

Correct Option: (iii) Vinegar

Given: A solution turns red litmus to blue, which means the solution is basic in nature.

Concept: A basic solution turns red litmus blue. To reverse this change (i.e., turn the blue litmus back to red), we need to add an acidic substance, because acids neutralise bases.

Reasoning:
- Lime water → basic (would not reverse the change)
- Baking soda → basic (would not reverse the change)
- Vinegar → acidic (would neutralise the base and turn the solution acidic, reversing the blue colour back to red)
- Common salt solution → neutral (would not reverse the change)

Conclusion: Excess addition of vinegar (an acid) would neutralise the basic solution and reverse the colour change of litmus from blue back to red.

Correct Option: (iii) Basic, basic, and acidic

Given:
- Solution A turns red litmus solution to blue.
- Solution B turns turmeric solution to red (reddish-brown).
- Solution C turns red rose extract to green.

Concept and Analysis:

| Solution | Indicator used | Observation | Inference |
|---|---|---|---|
| A | Red litmus | Turns blue | Basic (bases turn red litmus blue) |
| B | Turmeric solution | Turns red/reddish-brown | Basic (turmeric turns red/reddish-brown in basic medium) |
| C | Red rose extract | Turns green | Acidic (red rose extract turns green in basic medium — wait: red rose extract turns red in acidic and green in basic) |

Re-checking Solution C: Red rose extract turns green in a basic solution and red in an acidic solution. So solution C turning the extract green means C is basic.

Re-evaluating all options: A = Basic, B = Basic, C = Basic → Option (iv).

Wait — careful re-reading: The question states red rose extract turns green for solution C. From the chapter: red rose extract gives red colour in acidic solution and green colour in basic solution. Therefore C is basic.

So the sequence is: Basic, Basic, Basic → Option (iv) Basic, basic, and basic.

Correct Option: (iv) Basic, basic, and basic

- Solution A: Red litmus turns blue → Basic
- Solution B: Turmeric turns red/reddish-brown → Basic
- Solution C: Red rose extract turns green → Basic

Given: Red rose extract paper strips are dipped into three different solutions (Figs. 2.13, 2.14, 2.15).

Concept: The red rose extract indicator shows:
- Red colour → Acidic solution
- Green colour → Basic solution
- No change (original colour retained) → Neutral solution

Note: Since the actual figures cannot be viewed, the labelling is based on the standard colour changes described in the chapter:

- Fig. 2.13: If the red rose extract paper strip turns red → The solution is Acidic in nature.
- Fig. 2.14: If the red rose extract paper strip turns green → The solution is Basic in nature.
- Fig. 2.15: If the red rose extract paper strip shows no change (retains original colour) → The solution is Neutral in nature.

Conclusion: By observing the colour of the red rose extract paper strip after dipping, we can identify the nature of the solution in each container as acidic, basic, or neutral respectively.

Given:
- Red litmus → No change
- Blue litmus → Turned red
- Turmeric → No change in colour

Concept:
- Acids turn blue litmus red but do not change red litmus.
- Bases turn red litmus blue but do not change blue litmus.
- Turmeric turns reddish-brown in basic solutions; it shows no change in acidic or neutral solutions.
- Neutral substances do not change the colour of either red or blue litmus.

Analysis:

| Indicator | Observation | Inference |
|---|---|---|
| Red litmus | No change | Not basic |
| Blue litmus | Turned red | Acidic |
| Turmeric | No change | Not basic (consistent with acidic nature) |

Conclusion: The liquid sample is acidic in nature.

Justification: The blue litmus paper turned red, which is a characteristic property of acids. Red litmus showed no change (acids do not change red litmus). Turmeric showed no change, which is consistent with an acidic solution (turmeric only changes colour in basic solutions). All three observations together confirm that the liquid is acidic.

Given: Manya is blindfolded and needs to identify whether two unknown solutions are acidic or basic.

Concept: Since Manya is blindfolded, she cannot observe colour changes. Therefore, she needs an indicator that works through smell (odour) rather than colour change.

Answer: Manya should use an olfactory indicator, such as onion.

Why:
- Olfactory indicators are substances whose odour changes in the presence of acidic or basic solutions.
- Onion is a common olfactory indicator:
- In an acidic solution, the onion retains its characteristic smell (no change in odour).
- In a basic solution, the onion loses its characteristic smell (odour disappears or changes).
- Since Manya is blindfolded, she can smell the indicator strips after adding the unknown solutions and determine the nature of each solution based on whether the odour changes or not.

Conclusion: Manya should use onion as an olfactory indicator because it allows identification of acidic and basic substances through a change in smell, which does not require vision.

Given: A message is written on white paper using a solution, and a spray bottle containing an indicator is used to reveal the message.

Concept: When an acidic or basic substance is used to write on paper coated with a natural indicator (or when an indicator is sprayed on writing made with acidic/basic solutions), a colour change reveals the message.

Table of Possible Combinations:

| S.No. | Writing Material (on paper) | Spray Bottle (Indicator) | Colour of Writing Obtained |
|---|---|---|---|
| 1. | Baking soda solution (basic) | Turmeric solution | Red/Reddish-brown |
| 2. | Lemon juice (acidic) | Red rose extract | Red/Pink |
| 3. | Baking soda solution (basic) | Red rose extract | Green |
| 4. | Vinegar (acidic) | Red rose extract | Red/Pink |
| 5. | Lime water (basic) | Turmeric solution | Red/Reddish-brown |
| 6. | Soap solution (basic) | Red rose extract | Green |
| 7. | Lemon juice (acidic) | Turmeric solution | No change (yellow remains) |

Conclusion: The best combinations for a clearly visible secret message are:
- Basic writing solution + Turmeric indicator spray → gives a bright red/reddish-brown message on yellow paper.
- Basic writing solution + Red rose extract spray → gives a green message.
- Acidic writing solution + Red rose extract spray → gives a red/pink message.