Simply put, India is overpopulated.
Can you imagine how nice the place could be if there was say....25% of the population?
How much less pollution and issues would be there?
Sure, I can imagine it. I'm wondering how much thought you've actually put into it, though. How would you advise they achieve this goal of yours? The current population of India is something over 1,200,000,000, so that's over 900 million "extra" people. A lot of bodies to be disposed of, even if they obligingly line up for firing squads, march themselves over cliffs or whatever. A fair amount of pollution and issues right there, assuming the trivial obstacle of the instinct to survive could be magically be erased in nearly a billion people's minds.
Still, assuming you can do that, there are the economic / social repercussions of that many people suddenly absent from jobs like power generation and distribution, hospital staff, schools, law enforcement... a few issues there, too.
A natural disaster (or series of disasters) that killed that many people would certainly not confine itself to a single country. And India isn't that far from Australia, geographically speaking. You might think about that when you indulge in such fantasies.