Question

Grill of the door old windows are always painted before they are used give scientific reason

Answer 1

i. Usually grills of doors and windows are made of iron.
ii. Iron objects get rusted on exposure to moist air.
iii. Since air always contains moisture, iron grills get rusted.
iv. Painting iron objects prevents rusting, hence iron grills of doors and windows are painted before they are used

Answer 2

It is done to prevent corrosion of the Iron grills . Iron gets corroded on exposure to air , because of oxygen . Rust is basically oxidized Iron .