Detailed Instructions: This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
Q: Passage: In 1790, the first federal population census was taken in the United States. Enumerators were instructed to classify free residents as white or "other." Only the heads of households were identified by name in the federal census until 1850. Native Americans were included among "Other;" in later censuses, they were included as "Free people of color" if they were not living on Indian reservations. Slaves were counted separately from free persons in all the censuses until the Civil War and end of slavery. In later censuses, people of African descent were classified by appearance as mulatto (which recognized visible European ancestry in addition to African) or black.
A:
What year was the last federal population census taken in the United States?