The correct answer is C. Hisar.
Unclassified forests are forests that do not fall under any of the other categories of forests, such as reserved forests, protected forests, or village forests. They are often found in areas that are not suitable for agriculture or other human activities.
In Haryana, the district of Hisar has the maximum area under unclassified forests. This is because Hisar is located in the northern part of the state, which is a semi-arid region. The land in this region is not suitable for agriculture, and so it has been left to develop into forests.
The other options are incorrect because they do not have as much area under unclassified forests as Hisar. Kaithal is located in the southern part of the state, which is a more fertile region. Rohtak is located in the central part of the state, and Panchkula is located in the southern part of the state. All of these districts have some area under unclassified forests, but not as much as Hisar.