Before India gained independence, several individual attempts were made to estimate the country's national income to highlight the economic condition of the people under colonial rule.
Step 1: Analyze the options.
(A) M. S. Swaminathan: Known as the "Father of the Green Revolution in India," his work focused on agriculture and food security in the post-independence era.
(B) K. C. Pant: A prominent Indian politician and former minister who served in various capacities much later in independent India.
(C) Dadabhai Naoroji: Known as the "Grand Old Man of India," he was the first to attempt an estimation of national income in 1867–68. He famously authored "Poverty and Un-British Rule in India," where he put forward the "Drain of Wealth" theory.
(D) Prof. Keynes: John Maynard Keynes was a British economist whose theories (Keynesian economics) changed the practice of macroeconomics globally, but he did not calculate India's national income before independence.
Step 2: Conclusion.
Dadabhai Naoroji is the pioneering figure who first calculated India's national income to demonstrate the economic exploitation by the British.
Final Answer:
\[
\boxed{(C) \, \text{Dadabhai Naoroji}}
\]