Explanation:

- The Battle of Chausa took place between the Mughal emperor Humayun and Sher Shah Suri.

- It occurred on 26 June 1539.

1. 1639: This is long after the battle occurred. The 17th century involved different contexts and figures in Indian history.

2. 1539: This is the correct year when the battle took place. Humayun faced defeat against Sher Shah Suri.

3. 1729: This is much later in history, within the 18th century, and unrelated to this battle's timeframe.

4. 1440: This predates the battle significantly, as it belongs to the 15th century, when neither Humayun nor Sher Shah were born.