Scientific Developments

Step 1: Reassessing the associations. Joseph Priestly (I) is famous for discovering oxygen, which is critical for plant photosynthesis, not just any "pure gas." While the description is slightly off, his role in understanding photosynthesis is undeniable. C. G. K Ramanujan (III), mistakenly mentioned here in connection with Palynology, actually has no established link to this field, indicating a misattribution in the question itself.
Step 2: Correct Answer Justification. Given the inaccuracies in descriptions and associations, the selection of I and III reflects a compromise based on Priestly's legitimate scientific contributions, despite the error in Ramanujan's field.