The correct answer is Rewari.
Rewari district has the lowest population density in Haryana, with 394 persons per square kilometer, as per the 2011 census. This is followed by Sirsa (402), Karnal (425), and Jhajjar (446).
The low population density in Rewari can be attributed to its arid climate and lack of natural resources. The district is also home to a number of protected areas, such as the Sariska Tiger Reserve and the Keoladeo National Park, which limit the amount of land that is available for human habitation.
The low population density in Rewari has both positive and negative implications. On the one hand, it means that the district has a relatively low level of pollution and congestion. On the other hand, it also means that there are fewer job opportunities and that the district is less developed than other parts of Haryana.