------------------- if one is from India and has valid Indian passport then cant he/she enter India with Indian passport even if got US citizenship? How do the India immigration officer know that you got US citizenship?? If one is US citizen one can also get passport through US consulate or US embassy in India
In India, both arrival/departure are recorded (for all, including Indian nationals). If you enter India using Indian passport and:
a) try to leave using US passport:
you can get in trouble at airport because there will be no record of your arrival.
b) try to leave on Indian passport:
you will need green card else airline will not board you OR immigration officer may not clear you.