West Champaran is the district in Bihar that touches the boundary of both Uttar Pradesh and Nepal.

Explanation:

Location of West Champaran:
West Champaran is located in the northern part of Bihar, India. It is situated on the border of Nepal and shares its boundary with the Indian state of Uttar Pradesh.

Geographical Factors:
West Champaran is strategically located in the Terai region, which is a narrow strip of land at the foothills of the Himalayas. This region is known for its fertile plains and is prone to flooding due to the presence of several rivers, including the Gandak, which flows through the district.

Boundary with Uttar Pradesh:
West Champaran shares its border with Uttar Pradesh on its eastern side. It is bounded by the districts of Gorakhpur and Deoria in Uttar Pradesh. The border between West Champaran and Uttar Pradesh is demarcated by the Gandak River, which acts as a natural boundary between the two states.

Boundary with Nepal:
West Champaran also shares its boundary with Nepal on its northern side. The district is bordered by the Parsa district of Nepal. The border between West Champaran and Nepal is marked by the Rapti River, which forms a natural boundary between the two regions.

Importance of the Border:
The border of West Champaran with Uttar Pradesh and Nepal holds strategic and economic significance. It facilitates trade and cultural exchanges between the regions. The border areas serve as important transit points for people and goods traveling between Bihar, Uttar Pradesh, and Nepal.

Conclusion:
In conclusion, West Champaran is the district in Bihar that touches the boundary of both Uttar Pradesh and Nepal. Its location in the Terai region and the presence of natural boundaries like the Gandak River with Uttar Pradesh and the Rapti River with Nepal make it an important border district.