Question

Rima wrote a secret message in a paper using a solution X. Neha was able to read it as the letters turned green when rubbed with a solution Y. Identify X and Y.

• A. X - Vinegar
  Y - Phenolphthalein
• B. X - Lime water
  Y - Phenolphthalein
• C. X - Soap solution
  Y - Vinegar
• D. X - Soap solution
  Y - Red cabbage juice

Answer 1

The correct option is D X - Soap solution

Y - Red cabbage juice
Indicators are substances that help us to distinguish between acids and bases through colour change.
The following table depicts the colour change observed when these indicators are added in acidic or basic medium: $$\begin{array}{cccc}\text{Indicator}& \text{Colour of the Indicator}& \text{Colour in Acidic Medium}& \text{Colour in Basic Medium}\\ \text{Methyl orange}& \text{Orange}& \text{Pale pink}& \text{Pale yellow}\\ \text{Phenolphthalein}& \text{Colourless}& \text{Colourless}& \text{Pink}\\ \text{Turmeric}& \text{Yellow}& \text{Yellow}& \text{Red}\\ \text{Red cabbage}& \text{Purple}& \text{Red}& \text{Green}\end{array}$$From the above table it is clear that the letter was written using soap solution as it turned green when red cabbage juice was rubbed over it.