Falling dependency ratio can be a source of economic growth and prosperity for a country due to several reasons, which are discussed below:

Increase in Working-Age Population
As the dependency ratio falls, the proportion of the working-age population increases. This means that there are more people who are capable of contributing to the economy by working, paying taxes, and saving for the future. This can lead to an increase in the overall productivity of the economy, which can drive economic growth.

Increase in Savings and Investments
With a lower dependency ratio, individuals are likely to have fewer financial obligations towards dependents, such as children and elderly parents. This can lead to an increase in savings and investments, which can further stimulate economic growth.

Increase in Consumer Spending
With more people in the working-age population, there is likely to be an increase in consumer spending. This can lead to an increase in demand for goods and services, which can create more job opportunities and stimulate economic growth.

Reduced Burden on Government
A falling dependency ratio can reduce the burden on the government to provide for dependents, such as healthcare, education, and social security. This can free up resources that can be invested in other areas, such as infrastructure development, which can further stimulate economic growth.

Conclusion
In conclusion, falling dependency ratio can be a source of economic growth and prosperity for a country. By increasing the working-age population, savings, investments, and consumer spending, and reducing the burden on the government, it can provide a favorable environment for economic growth.

A rising dependency is a cause for worry in countries that are facing an aging population, since it becomes difficult for a relatively smaller proportions of working age people to carry the burden of relatively larger proportions of dependent.              (I hope it will be a right answer for this question)