Explanation:

- Option 1: What is supposed to be

- Normative economics, not positive economics, deals with "what is supposed to be." It involves value judgments and opinions about economic policies.

- Option 2: Central problems of an economy

- This statement covers economic problems like scarcity, choice, and opportunity cost, which all economies face. It's more about fundamental economic issues, not specifically positive economics.

- Option 3: What is

- Correct Answer: This defines positive economics. It focuses on describing and explaining economic phenomena based on facts, without involving value judgments.

- Option 4: What will be

- This relates to predictive aspects of economics, analyzing future outcomes based on current data. It leans on positive economic analysis but focuses on forecasting.

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