Answer : 1. "Rigveda"
Explanation :

The first mention of Bharat Jana is found in the Rig Veda.

1. Veda: Rigveda

2. Division: Third

3. Mention: Mention of Bharat, son of Vishwamitra.

4. Significance: India was named 'Bharat' after the people of India.

Additional Information:

1. The seventh mandala of the Rig Veda describes the role of the Bharatas in the war of the ten kings (Dasharajya Yuddha) in which King Sudas of their Tritsu branch was victorious.

2. Due to this, they became dominant over the Indo-Aryans and the Indians were able to move beyond the Indus River region and settle in the area of Kurukshetra.

3. During that period, the political system was changing from being republican based on tribes to being centred on kings.