Almost surely these are propellant tanks, probably hydrazine which is very nasty shit. Usually those don’t survive intact, because, you know, they hold fuel and oxidizer. They’re a literal self contained bomb.

Even after being used there is usually some residual fuel that ends up exposing/burning up on the day down.

According to BBC:

India’s space agency spokesman later told the BBC that it was from one of its Polar Satellite Launch Vehicles (PSLV).