Data was obtained from the health department about number of people getting disease X and from another department about fat consumption of a country. From this it was concluded that country with higher fat consumption had higher patients of disease X. This is an example of:
|B||Cross sectional study|
In Ecological or correlational studies the basic unit of the study is the entire population, hence the question mentions about the country on whom the results of the study will be applicable and not every individual of that country.
All the other option in the question individual members of the population are taken into account while drawing conclusions about the cause effect relationship.