The correct answer is B. Lahaul and Spiti.
As per Census 2011, the male literacy rate in Lahaul and Spiti district of Himachal Pradesh is 71.7%, which is the lowest among all the districts of the state. The male literacy rate in Chamba district is 80.1%, in Kangra district is 84.7%, and in Solan district is 85.4%.
The low male literacy rate in Lahaul and Spiti district can be attributed to a number of factors, including the remoteness of the district, the high altitude, and the harsh climate. The district is also home to a number of tribal communities, who have traditionally had lower literacy rates than the rest of the population.
In recent years, the government has taken a number of initiatives to improve literacy rates in Lahaul and Spiti district. These initiatives include the construction of new schools, the provision of scholarships, and the training of teachers. The government has also launched a number of awareness campaigns to encourage people to send their children to school.
As a result of these initiatives, the literacy rate in Lahaul and Spiti district has been increasing in recent years. However, the district still has a long way to go to achieve universal literacy.