The Central Bank Monetary policy instrument by which it buys and sells securities is called

The Central Bank monetary policy instrument by which it buys and sells securities is called "Open market operation". Open market operation refers to the process by which the Central Bank of a country buys or sells government securities in the open market, i.e., from banks, financial institutions, or the general public. When the Central Bank buys securities, it injects money into the economy, which increases the money supply and reduces the interest rates. This is because the banks will have more money to lend out to individuals and businesses, and they will do so at a lower interest rate. On the other hand, when the Central Bank sells securities, it reduces the money supply in the economy, which increases the interest rates. This is because the banks will have less money to lend out, and they will do so at a higher interest rate to maintain their profit margins. In summary, open market operations are an important tool for the Central Bank to manage the money supply in the economy and influence the interest rates.