Explanation:

- The Atal Tunnel, named by PM Modi in December 2019, passes through the Rohtang Pass in Himachal Pradesh.

- It's a remarkable engineering feat, stretching 8.6 km in length.

- The tunnel reduces the distance between Leh and Manali by 46 km, thus significantly improving travel efficiency and connectivity.

- Shimla is not directly connected to Leh by the tunnel, so this option is incorrect.

- Srinagar, while another major city in the region, is not affected by this tunnel in terms of distance reduction.

- Ladakh is a broader region where Leh is a key city, but the tunnel specifically references Leh's distance to Manali.

- Dehradun is geographically unrelated to the tunnel in terms of distance impacts.

Correct Answer: Option 2, Manali