With an increase in population, we generally observe a rightward shift in the market demand curve. This is because more people means more potential consumers in the market. As the population grows, the overall demand for goods and services increases, which results in an upward shift of the market demand curve.
However, it’s important to note that individual demand curves for specific consumers may not change in the same manner. Each individual’s demand might remain stable, even as the overall market demand rises, due to personal preferences or income levels. In this way, we can say that there’s no shift in each individual’s demand curve, but rather, an external factor (population increase) is influencing the overall market demand.
To sum up, the correct answer would be c: a rightward shift in the market demand curve as it encompasses the aggregate effect of a population increase on demand.