2 mL of ethanoic acid was taken in each of test-tube I and test-tube II. A red litmus paper was introduced in test-tube I and a pH paper was introduced in test-tube II. The experiment was performed by four students A, B, C and D, they reported their observations as given below :

Student	Action on red litmus	Action of pH paper
ABCD	Turned blueRemains unchanged Turned blueRemains unchanged	Turned pinkTurned greenTurned blueTurned pink

The correct set of observations was made by the student :(1) A       (2) B
(3) C       (4) D"

Correct answer: (4) D

Explanation: The observation of student D on the action of litmus is correct as red litmus remains unchanged in the presence of ethanoic acid (acid changes blue litmus to red) and pH paper will turn pink as ethanoic acid is a weak acid.