Question

An aqueous solution turns red litmus blue.Excess addition of which of the following would reverse the change?

Baking powder
Slaked lime
Ammonium hydroxide
Vinegar

Answer 1

Answer:

Excess addition of vinegar causes the reverse

Explanation:

We know that,

Basic or alkaline solutions turn red litmus to blue

Acidic solutions turn blue litmus to red

Here,

red litmus is changing to blue that means the aqueous solution used is basic in nature

So for the reverse to happen that is, for blue litmus to change into red we have to add an acid

In the given options,

Baking powder or NaHCO₃ is basic

Slaked lime or Ca(OH)₂ is basic

Ammonium hydroxide or NH₄OH is also basic

only

Vinegar or acetic acid or CH₃COOH is acidic

Hence we have to add vinegar in excess to turn blue litmus back to red

Answer 2

The correct answer is option (b) slaked lime

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