The correct statement is 2 only: "Only some cyclones develop an eye." This is accurate because not all cyclones, specifically weaker ones or tropical storms, form a distinct eye, which is a region of calm typically found in stronger hurricanes. Statement 1 is incorrect as jet streams occur in both the Northern and Southern Hemispheres, while statement 3 is also incorrect because the temperature in the eye of a well-developed cyclone is actually warmer than the surrounding clouds, often around 10°C or more, due to descending air compressing and warming. This conceptual understanding of cyclones and atmospheric dynamics is crucial for UPSC-level preparedness.