The correct answer is (d) Income Tax.
Income tax is a tax levied on the income of individuals and businesses. It is the most important source of tax revenue for the Union Government. In 2009-10, income tax accounted for 39.7% of the total tax revenue of the Union Government.
Service tax is a tax levied on the value of services provided. It is a relatively new tax, having been introduced in 1994. Service tax is the second most important source of tax revenue for the Union Government. In 2009-10, service tax accounted for 18.2% of the total tax revenue of the Union Government.
Union excise duties are taxes levied on goods produced or manufactured in India. They are the third most important source of tax revenue for the Union Government. In 2009-10, union excise duties accounted for 17.9% of the total tax revenue of the Union Government.
Corporation tax is a tax levied on the profits of companies. It is the fourth most important source of tax revenue for the Union Government. In 2009-10, corporation tax accounted for 14.2% of the total tax revenue of the Union Government.
The other options are not as important as income tax as a source of tax revenue for the Union Government.