The best statement that reflects the chief purpose of the 'Constitution' of a country is:

Option 3: It defines and limits the powers of government.

The primary purpose of a constitution is to establish the fundamental principles, structures, and processes of a government. It serves as a supreme law that defines the powers, functions, and limitations of the government and its various branches. By clearly delineating the authority and responsibilities of different branches of government, such as the legislature, executive, and judiciary, the constitution ensures a system of checks and balances.

The constitution sets out the framework for governance, including the division of powers between the central and regional governments, the rights and freedoms of individuals, the principles of democracy, and the mechanisms for lawmaking and decision-making. It provides a legal basis for the functioning of the government, establishes the rights and obligations of citizens, and safeguards the rule of law.

While the other options mentioned in the question are important aspects related to the constitution, such as the creation of political offices and a government (Option 2), determining the objective for making necessary laws (Option 1), and securing social justice, social equality, and social security (Option 4), they are not the chief or primary purpose of a constitution. The primary focus of a constitution is to define and limit the powers of government to ensure a balanced and accountable system of governance.