Which one of the following can be used as an acid–base indicator by a visually impared student?
(C) Vanilla essence
(D) Petunia leaves
For visually impaired students, we need an Olfactory indicator . Which smells different in acids and bases.
Vanilla essence can be used as an acid-base indicator by visually impaired students as it is an olfactory indicator whose odour changes in acidic or basic media.
So, the correct answer is (c) vanilla essence