Due to rusting, the weight of iron

The correct answer is (b). Rusting is a chemical reaction that occurs when iron is exposed to oxygen and water. The reaction produces iron oxide, which is a red, flaky substance. Iron oxide is less dense than iron, so the weight of the iron decreases when it rusts.

Option (a) is incorrect because rusting does not cause the weight of iron to increase. Option (c) is incorrect because rusting does cause the weight of iron to change. Option (d) is incorrect because the weight of iron does change when it rusts.