In India, the tax proceeds of which one of the following as a percentage of gross tax revenue has significantly declined in the last five years?

1. The question asks which tax proceeds, as a percentage of gross tax revenue in India, had significantly declined in the last five years (relative to 2010). 2. We need to consider the trends in major central taxes in the period roughly from 2005 to 2010. 3. (A) Service tax: Introduced in 1994 and expanded significantly in the 2000s, its share in gross tax revenue was generally increasing during this period. 4. (B) Personal income tax: Its share tended to be relatively stable or slightly increasing with economic growth and widening tax base. 5. (C) Excise duty: Union Excise duties, levied on manufacturing, were historically a major source of revenue. However, with tax reforms, gradual reduction in rates, and the later move towards GST (though GST came after 2010, the trend of rationalizing indirect taxes was present), the relative share of Union excise duties in the total tax pool showed a declining trend during this period compared to direct taxes and service tax. 6. (D) Corporation tax: Its share was generally robust or increasing during periods of good corporate performance. 7. Therefore, Excise duty is the most likely tax whose share in the gross central tax revenue saw a significant decline in the five years leading up to 2010.