The correct answer is D) Aluminum. Aluminum is prone to developing a white-gray powdery deposit, which is a result of oxidation. This white powdery substance is aluminum oxide, formed when the aluminum metal reacts with oxygen in the air. This oxide layer helps protect the underlying aluminum from further corrosion, but it can give the metal a dull, whitish appearance. The other options are incorrect because: Steel does not typically form a powdery deposit, but may develop rust; magnesium can form a white or gray powdery deposit, but it is more likely to be magnesium oxide; and magnetite is a type of iron oxide, which has a black or dark gray color, not a white-gray powdery appearance.