Correct Option: B. Reserve requirements Detailed Explanation: The Central Bank of Nigeria (CBN) employs various tools to regulate and control the activities of commercial banks, ensuring stability in the financial system and the economy. Among these tools, reserve requirements are considered the most effective for several reasons.

1. Definition of Reserve Requirements:
2. Reserve requirements refer to the minimum amount of reserves that commercial banks must hold against their deposit liabilities. This is usually expressed as a percentage of the bank's total deposits. For example, if the reserve requirement is set at 10%, a bank with ₦1,000,000 in deposits must hold ₦100,000 in reserve.
3. Mechanism of Control:
4. By adjusting the reserve requirement, the CBN can directly influence the amount of money that banks can lend. If the CBN increases the reserve requirement, banks must hold more money in reserve and can lend less, which reduces the money supply in the economy. Conversely, if the reserve requirement is lowered, banks can lend more, increasing the money supply.
5. Impact on Monetary Policy:
6. Reserve requirements are a powerful tool for implementing monetary policy. By controlling the money supply, the CBN can influence interest rates, inflation, and overall economic activity. This makes reserve requirements a critical tool for achieving macroeconomic stability.
7. Stability and Predictability:
8. Reserve requirements provide a stable and predictable framework for banks. Banks can plan their lending and investment strategies based on the reserve requirements set by the CBN, which helps in maintaining liquidity and solvency in the banking system.

Why Other Options Are Weaker:

• A. Open Market Operations:
• Open market operations involve the buying and selling of government securities in the open market to regulate the money supply. While effective, they are often more indirect and can be influenced by market conditions. The impact of open market operations can take time to materialize, making them less immediate compared to reserve requirements.
• C. Bank Rate:
• The bank rate is the interest rate at which the central bank lends money to commercial banks. While it influences borrowing costs and can affect lending behavior, it does not directly control the amount of money banks must hold in reserve. Changes in the bank rate can also have a delayed effect on the economy.
• D. Directives:
• Directives are instructions issued by the central bank to commercial banks regarding their operations. While they can be useful for specific regulatory purposes, they lack the systematic and quantitative control that reserve requirements provide. Directives may also be less flexible and can lead to compliance issues.

Summary of Key Points:

• Reserve Requirements: The most effective tool for controlling commercial banks, directly influencing their lending capacity.
• Immediate Impact: Changes in reserve requirements have a direct and immediate effect on the money supply and banking operations.
• Stability: Provides a predictable framework for banks, aiding in liquidity management.
• Comparison with Other Tools: Open market operations and bank rates are less direct and can have delayed effects, while directives lack the quantitative control of reserve requirements.

This understanding of reserve requirements and their role in monetary policy is crucial for anyone studying economics, particularly in the context of the Central Bank's functions.