On adding a few drops of universal indicator solution to three unknown colourless solutions P, Q, and R taken separately in three test-tubes shown in the diagrams, a student observed the changes in colour as green in solution P, red solution Q and violet in solution R.

The decreasing order of the pH of the three solution is :
(1) P > Q > R
(2) R > P > Q
(3) Q > P > R
(4) R > Q > P

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Solution

The universal indicator shows a wide range of colour difference for acids and bases. Acids show red to yellow colour, bases show blue to indigo, and neutral molecules show green colour. P shows green colour, so it is neutral, Q shows red colour, so it is an acid and R shows violet colour, so it is a base.
So, from the above discussion, we can arrange the given molecules in decreasing order: R > P > Q.

Hence, the correct answer is option 2.

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