The correct answer is: Kanyakumari – Dibrugarh Vivek Express.
The Kanyakumari – Dibrugarh Vivek Express is a superfast train that runs between Kanyakumari in Tamil Nadu and Dibrugarh in Assam. It is the longest train in India, with a route length of 4,273 km. The train covers the distance in 82 hours and 55 minutes. It has 24 coaches, including 1 AC 1st class, 2 AC 2 tier, 3 AC 3 tier, 12 sleeper class, 3 general class and 1 pantry car. The train is operated by the Indian Railways.
The other options are incorrect because they are not as long as the Kanyakumari – Dibrugarh Vivek Express. The Howrah – Jammu Tawi Himgiri Express has a route length of 3,422 km, the Kanyakumari – Jammu Tawi Himsagar Express has a route length of 3,349 km, and the Guwahati – Tiruvananthapuram Express has a route length of 2,825 km.