For a long period before later revisions, which of the following was taken as the base year for the official computation of national income and GDP in India?

Introduction / Context:
National accounts statistics are periodically updated by changing the base year so that GDP and national income figures reflect a more recent structure of the economy. Knowing which year is taken as the base year at different times is a common exam question in Indian economy. This question asks about an earlier widely used base year that preceded later revisions, focusing on a period when 1999-2000 was the benchmark for calculating national income and GDP at constant prices.

Given Data / Assumptions:

- The question is about the base year used for national income computation in India in an older series.- Options list several candidate years around the 1990s and early 2000s.- We assume awareness that base years have changed over time (e.g., 1993-94, 1999-2000, 2004-05, 2011-12).

Concept / Approach:
A base year in national accounts is a year chosen as a reference point for measuring real growth by holding prices constant at that year's level. India has updated this base year multiple times. For a significant period, national income and GDP at constant prices were calculated using 1999-2000 as the base year, before a later shift to 2004-05 and then to 2011-12. Many exam questions from that era refer to 1999-2000 as the base year, and it remains an important fact in historical context. Hence, among the given options, 1999-2000 is the correct answer for that earlier base year.

Step-by-Step Solution:
1. Recall that India's national accounts earlier used 1993-94 as a base year and later shifted to 1999-2000.2. Understand that this base year was again revised to 2004-05 and then to 2011-12 in subsequent updates.3. Note that the question refers to the base year used for computation, without specifying the very latest revision, and provides 1999-2000 as one of the options.4. Recognise that 1990-91 and 2000-01 were not used as major national income base years in the standard sequence for exam purposes.5. Select 1999-2000 as the appropriate base year being referred to in this question.

Verification / Alternative check:
Indian economy textbooks and Economic Survey summaries from the period of the 1999-2000 base revision clearly state that GDP and national income at constant prices were being rebased to 1999-2000. Later, official documents describe subsequent rebasing to 2004-05 and 2011-12. Exam oriented materials carefully track these changes, and many older multiple choice questions highlight 1999-2000 as the then prevailing base year, confirming its relevance in this context.

Why Other Options Are Wrong:
- 1990-91: not a standard base year in the widely cited national accounts revision sequence.- 1993-94: was an earlier base year but was replaced by 1999-2000 in a later revision, and the question focuses on a more recent base in that sequence.- 2000-01: not used as the primary base year in official rebasing cycles discussed in most exam books.- 2004-05: became a later base year, but the question refers to an earlier base that had been used widely for some time.

Common Pitfalls:
Students often get confused between multiple base years because revisions occur every few years and exam questions are drawn from different time periods. Another frequent mistake is to simply pick the latest base year they remember, even when the question is clearly about an earlier series. To minimise confusion, memorise the sequence: 1993-94, then 1999-2000, then 2004-05, and then 2011-12. When you see older options like those in this question, you can accurately identify 1999-2000 as the correct earlier base year being tested.

Final Answer:
For a significant period, India used 1999-2000 as the base year for computing national income and GDP at constant prices.