Hello candidate,

This is an example of balanced chemical Reaction where two moles of iron reacts with two moles of water in the presence of one mole of Oxygen to healed 2 moles of ferrous hydroxide. So, two moles of iron requires two moles of water and one mole of Oxygen, but according do the given quantities it seems that oxygen is the limiting reagent based on the the proportions. So, 4 grams of oxygen means 1 by 4 mole of Oxygen produces 0.5 mole of ferrous hydroxide which is equal to 45 grams.

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