Option 1: Tiruvananthapuram and Guwahati - This option is not correct. While Tiruvananthapuram is located in the southernmost part of India, Guwahati is located in the northeastern part of the country. Hence, the two cities are not connected by the longest passenger rail route in India.
Option 2: Kanyakumari and Jammu Tawi - This option is correct. Kanyakumari is the southernmost tip of mainland India, and Jammu Tawi is located in the northernmost part of the country. Connecting these two points by rail would cover a significant distance, making it the longest passenger rail route in India.
Option 3: Jammu Tawi and Guwahati - This option is not correct. While this route would cover a considerable distance from the northernmost part of India to the northeastern part, it is not the longest passenger rail route in India.
Option 4: Tiruvananthapuram and Jammu Tawi - This option is not correct. While this route would cover a substantial distance from the southernmost part of India to the northernmost part, it is not the longest passenger rail route in India.
In conclusion, option 2 - Kanyakumari