Mrinal sets up an experiment: one iron nail in a dry, closed bottle; one in a bottle of boiled…
Mrinal sets up an experiment: one iron nail in a dry, closed bottle; one in a bottle of boiled water with a layer of oil on top; and one in a little ordinary water, open to the air. Mrinal predicts that the nail completely under the boiled water and oil will rust the most, because rust is caused by water. Zubair says that nail will hardly rust at all. Whose prediction will come true?
Who do you think is right? Pick one.
The answer: Zubair is right, rusting needs both water and air
Why
Mrinal is correct that water matters — iron left out in the rain does rust, and a nail kept dry in a closed bottle stays shiny. But rusting needs two things together: water AND the oxygen in air. Boiling the water drives out the air dissolved in it, and the layer of oil stops fresh air from dissolving back in. So the nail in that bottle has plenty of water but almost no oxygen, and it hardly rusts. The dry nail has air but no water, so it hardly rusts either. The nail in ordinary water open to the air has both — and that is the one that rusts the most. Test: this is also why painting, oiling or greasing an iron gate or a bicycle chain prevents rust — the coating keeps air and moisture away from the iron. Zubair is right: the nail under boiled water and oil will barely rust, because rust needs air and water together.
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