Final answer:
The issue at the heart of a compromise between northern and southern states during the Constitutional Convention was counting slaves in the population.
Step-by-step explanation:
The correct answer is B. Counting slaves in the population.
During the Constitutional Convention, the issue of how to count slaves in the population became a major point of contention between the northern and southern states. The southern states wanted to include slaves in the population count to increase their representation in the House of Representatives, while the northern states argued that slaves should not be counted as they were considered property and not citizens.
To reach a compromise, known as the Three-Fifths Compromise, it was agreed that each slave would be counted as three-fifths of a person when determining representation in the House of Representatives and for taxation purposes.
Learn more about Compromises made during the Constitutional Convention