Four students were given colourless liquids A, B, C of water, lemon juice and a mixture of water and lemon juice respectively. After testing these liquids with pH paper, the following sequences in a colour change of pH paper were reported.
The correct sequence of observations is:

We shall now see in detail the pH and its changes in colour with different solutions.
pH is the one we all know and is defined as the negative logarithm of the hydrogen ion concentration in the solution.
We all are familiar with pH, which is defined as the negative logarithm of the concentration of hydrogen ions in the solution.
Varying solutions have different pH values. The pH value is low for acidic solutions and high for basic solutions.
Acidic solutions have a pH of less than 7, whereas basic solutions have a pH of greater than 7. The solution is neutral when the pH value is 7, which.
It is stated in the question above that four students received three solutions: Water is A, lemon juice is B, and a combination of water and lemon juice is C.
Now, since water is neutral, the pH colour for the neutral solution in pH paper is green and lemon juice is acidic in nature and thus the pH paper colour for this acidic solution is depending on the strength of acids where for the strong acids it is red in colour.
Hence, the correct answer is Green, red and red.