Q.Why does India's per-capita income remain comparatively low even though its total GDP has been growing rapidly? Explain briefly.

Because per capita income divides national income by population, rapid population growth can offset even fast GDP growth, keeping the average per person low. …

Per Capita Income is defined as $PCI = \dfrac{\text{National Income}}{\text{Mid-year Population}}$. This formula shows that PCI depends not just on how fast the numerator (national income/GDP) grows, but also on the size and growth rate of the denominator (population).

India's total GDP has grown substantially over the decades, but with a very large population base, the same absolute increase in national income has to be divided among a much larger number of people than in a smaller country with comparable GDP growth. If population grows at a meaningful rate alongside GDP, a large part of the gain in national income is effectively absorbed by having to be shared across more people, so per capita income rises more slowly than GDP itself. …