Final answer:
The most accurate source for researching city populations during the industrial era is government census records, as they are comprehensive and meant to objectively measure population sizes and demographics.
Step-by-step explanation:
When researching information about the population of cities during the industrial era, the most accurate source would be government census records from the era. These records were official counts carried out by the government and are considered to be a reliable snapshot of population sizes and demographics of the time. In contrast, newspaper articles might contain journalistic bias or errors, oral history interviews with current residents are retrospective and may be influenced by personal memory, and social media posts from industrial workers (if they even existed as historical documents rather than contemporary accounts) would not provide a comprehensive view and could reflect personal experiences rather than empirical data.
For example, studying the growth of major cities such as New York and Chicago during the industrial era requires data that reflects the total population and its changes over time accurately. Government census records aim to measure exactly that, whereas other sources might only provide partial or anecdotal evidence.
Looking at primary sources, a diary entry by a person who lived in the period under discussion would be a primary source; it provides a first-hand account of events or daily life at that time. However, for population metrics specifically, official census records remain the gold standard.