Concept:Index numbers are statistical measures used to track changes in economic variables over time.Explanation:Index numbers serve multiple purposes in economics.They help in framing economic policies by providing data on price levels, production, etc.They are used to assess the purchasing power of money through price indices like the Consumer Price Index.They help adjust national income from nominal to real terms by accounting for inflation.Thus, all the given options are correct uses of index numbers.Answer:D. all the above