Question

What parameter does an indicator change, with change in the nature of the solution?
A.Colour
B.Odour
C.Both
D.None of these

Answer 1

An indicator is used in detection of my solution and its properties. Some common applications include detection of end points of titration. Universal indicators change their colour to indicate the approximate pH of the solution.

Complete Answer:
An indicator is a substance whose colour changes due to change in the pH of a solution. This is what we call acid-base indicators which are usually weak acids or weak bases but their conjugate base or acid form have different colours due to differences in their absorption spectra. We can see these indicators in our day to day life as well. One example is the colour of tea. The tea colour will darken in basic solution, whereas in acidic solution its colour becomes lighter. For example when we add lemon to black tea, the tea colour becomes lighter.
As mentioned earlier in the hint, indicators are used in detection of the end point of titration. The chemicals used in this detection are $phenolphthalein$ and $methyl$ orange. $phenolphthalein$ is used as an acid-base indicator. At a pH value $8.3 - 10$ it appears pink in colour, thus indicating basic solution, whereas in acidic solution it appears clear. $methyl$ orange when present in acidic solution appears red in colour. When $methyl$ orange is present in the basic solution, it turns yellow.
Thus it is clear from the above theory that as a solution turns acidic or basic the colour of the indicator changes and they have nothing to do with the odour.

Therefore the correct answer is option a.

Note:
Apart from the chemicals mentioned, we have natural indicators as well. Turmeric, inion, red cabbage, grape juice are such examples which help us determine whether a solution is acidic or basic in nature. Turmeric is yellow in acid but changes to red in basic.