Question

S1: Palaeobotany is the study of fossil plants preserved in rocks dating back in millions of years.
P. Records of the history of the world are contained in fossils.
Q. Through the ages, plants have evolved from simple to more complex forms.
R. First there were water plants then land plants appeared during the Paleozoic era.
S. But since the fossil remains appear locked in rock layers, they are closely related to the geologist area of investigation.
S6: The fossil plants indicate the age of the rock, and also point to facts regarding climate, temperature and topography.
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Answer 1

$S_1$ gives the definition of Palaeobotany. There is a clear sequence of Q followed by R as R gives an example of the evolution mentioned in Q. Similarly, there is a clear sequence of P followed by S as there is a link of fossils between them. Now, the sequence QRPS makes more sense than PSQR as there is no connection between statements S and Q. On the other hand, S is a good precursor to $S_6$ as $S_6$ mentions things like climate, temperature and topography that are closely related to the geologist's area of investigation.
So the answer is QRPS.