Step 1: Understanding the Concept:
Demographic data refers to statistical information about the characteristics of a population, such as age, gender, literacy rate, income, and geographic distribution. The question asks for the primary reason why this data is considered important.
Step 2: Detailed Explanation:
While all the given options are valid reasons for the importance of demographic data, the most crucial function, especially from a governance perspective, is its role in policy-making.
(A) It helps in the planning and implementation of State policies: This is the most direct and practical application. Governments use demographic data to make informed decisions about resource allocation, infrastructure development (schools, hospitals), social welfare programs, taxation, and economic planning. Without this data, governance would be based on guesswork.
(B), (C), and (D) are also true. Collecting such data is indeed a feature of modern states (B), provides a general overview (C), and is essential for academic analysis of population trends (D). However, these are secondary to the primary function of enabling effective governance and planning.
Step 3: Final Answer:
The fundamental importance of detailed demographic data lies in its utility for the effective planning and execution of state policies for the welfare of the population.