The correct answer is: Only conclusion II follows.
The statement gives the average number of persons per household in urban and rural areas, as well as the national average. It does not give any information about the population per unit area in either urban or rural areas. Therefore, we cannot conclude that the population per unit area in the rural areas is higher than in the urban areas.
However, the statement does give us information about the number of persons per household in each area. We can conclude that more persons live in the same household in rural areas as compared to those in urban areas. This is because the average number of persons per household is 7 in rural areas, while it is only 5 in urban areas.
Therefore, the only conclusion that follows from the statement is conclusion II.