Question

Why country like india require federlism

Answer 1

Federalism allows people living in different states with different needs and different interests to set policies suited to the people in their state, yet still come together with other states as one nation. 
Just as states have different physical resources, their populations have different interests and needs. If I try to force people in Massachusetts to adopt the divorce or child custody laws from Texas, they would quite reasonably protest that they should be allowed to govern themselves. 
There are limits on what states can do- they cannot pass laws that violate rights guaranteed