Final answer:
The world population is expected to reach 9 billion around the year 2050, according to the U.S. Census Bureau and United Nations' estimates.
Step-by-step explanation:
Based on projections by the U.S. Census Bureau and the United Nations' estimates, the world population is expected to reach 9 billion around the year 2050. While specific estimates may vary slightly, most sources converge on 2050 as the year when the population will hit this milestone.
In fact, historical data shows the progression in billions: 7 billion in 2012, 8 billion projected for 2028, and 9 billion by 2054. However, the consensus among demographers seems to align more closely with the 2050 mark.
Therefore, the correct answer to the question, 'What year will the population reach 9 billion?', based on the given options, would be 'C) 2050'.