Question

Why iron doesn't burn on heating but iron filings burn vigorously?

Answer 1

The mass of a small particle is such that the entire particle can be heatedto ignition temperature. An iron rod willnot burn as it has relatively very less surface area per unit mass but iron filings with more surface area per unit mass can burn in air and get converted to iron oxide.
hope it helped you,
mark me as brainlist

Answer 2

hi dear......

There may be two possibilities for vigorous burning of iron fillings:

The surface area of the fillings is much more than a block of iron.

The heat supplied to the iron fillings does not have a way to distribute itself through conduction, like in iron block, as the entire filling is surrounded by the flame, and thus, the iron fillings reach their ignition temperature but iron block does not.

hope I answered your question. !!!