Which financial institution ensures that a nation's economy remains healthy by controlling the amount of money circulating in the economy?

Commercial banks primarily focus on accepting deposits and providing loans to individuals and businesses. While they do contribute to the money supply through their lending activities, they do not have the authority to control monetary policy or directly manage the overall economy like a central bank does.

Private equity firms invest in private companies or acquire public companies to restructure and enhance their value before selling them for a profit. Their operations are geared towards investment returns rather than controlling the money supply or influencing monetary policy, making them unrelated to the health of a nation's economy.

Investment banks assist companies in raising capital and provide advisory services for mergers and acquisitions. They facilitate transactions in financial markets but do not play a role in monetary policy or the broader control of the money supply, which is the domain of central banks.