what happens to the weight of an iron bar after the iron rust?

Question

that is assuming that the rust does not fall of the bar

Answer 1

Oxidation of the Iron bar changes it to hydrated ferric oxide during the process of rusting. Oxygen and water of hydration in the chemical composition would cause its wieght to increase.
Thus its weight increases.

Answer 2

the weight of iron bar increases as there is some molecular weight of oxygen asrustis Fe2O3.H2O
but its density decreases as now it occupies a larger volume than before rusting

Answer 3

it changes and so does the mass because of the Oxide that changed its properties.