Option 1 -> While the passage mentions assembling large structures in orbit, this is a future application, not the main significance.
Option 2 -> The passage explicitly describes SpaDeX as a "technological milestone" that cements India's position among elite space nations.
Option 3 -> The passage refers to future space station operations, not a completed space station.
Option 4 -> The passage discusses space docking technology, not a new rocket series.
Hence, Option 2: A major milestone in India's space program -> The passage clearly states that SpaDeX "represents more than just a technological milestone" and is "a significant advancement in India's capabilities," placing India among elite nations in the global space race -> correct