The correct answer is (c) Population.
The Thirteenth Finance Commission of India was constituted on 28 February 2009 by the President of India, Pratibha Patil, to recommend the devolution of central taxes and duties to the states and union territories for the period 2010-2015.
The Commission assigned the highest weightage of 50% to population while recommending devolution of Union taxes amongst States. This was done on the basis of the principle of equity, which states that the resources of the Union should be shared among the States in proportion to their population.
The other factors considered by the Commission were fiscal capacity, fiscal performance, and special needs of the States. Fiscal capacity refers to the ability of a State to raise revenue from its own sources. Fiscal performance refers to the efficiency with which a State manages its finances. Special needs of the States refer to the additional resources that a State may need to meet its specific requirements, such as those arising from natural calamities or ethnic conflicts.
The Commission’s recommendations were accepted by the Government of India and implemented from 1 April 2010.