Step 1: Define obligatory functions.
Obligatory functions of the government refer to the essential responsibilities that a government must fulfill to ensure the well-being and safety of its citizens.
Step 2: Analyze the options.
- Option (a) is incorrect because providing education and health services, while important, is not always mandatory in all governmental systems.
- Option (b) is incorrect because the provision of pensions is a welfare measure, not an obligatory function.
- Option (c) is correct as maintaining internal law and order is a primary and obligatory function of any government to ensure the security and stability of the nation.
- Option (d) is incorrect because the provision of welfare measures, while essential, is typically not an obligatory function under all circumstances.
Step 3: Conclude.
Therefore, the correct answer is maintaining internal law and order, which is a fundamental and obligatory function of the government.
Final Answer: \[ \boxed{Maintaining \; internal \; law \; and \; order.} \]