Question

An element \[X\] on exposure to moist air turns reddish-brown and a new compound \[Y\] is formed. The substance \[X\] and \[Y\] are?
A.\[X={ }Fe\],\[Y={ }F{{e}_{2}}{{O}_{3}}\]
B.\[X={ }Ag\],\[Y{ }A{{g}_{2}}\]
C.\[X=Cu\],\[Y=CuO\]
D.\[X={ }Al\],\[Y{ }={ }A{{l}_{2}}{{O}_{3}}\]

Answer 1

Hint: Oxidation is the process in which a substance undergoes a reaction with oxygen, for instance when metals are exposed to air for a long period of time, a thin layer of metal oxide is formed on the surface of metal because of presence of oxygen in air.

Complete step by step answer:
Now looking at all the four options that have been provided in the question First one is \[F{{e}_{2}}{{O}_{3}}\]. This is a compound which is chemically named as Ferric Oxide. It is also known as Iron ($III$) oxide. The moment Iron is exposed to air, it forms Ferric Oxide.
The reaction is a simple oxidation reaction and is seen in most natural cases such as Rusting of iron. If you look clearly, Rust is a chemical reaction in which the rust is in Reddish Brown in Color.
The reaction which takes place can be expressed chemically in the following way,
\[Fe+{{H}_{2}}O+{{O}_{2}}\to F{{e}_{2}}{{O}_{3}}\]
When iron is reacted in moist air (\[{{H}_{2}}O+{{O}_{2}}\]) it gives reddish Brown in Color chemically named as ferric oxide.
If we consider option B, the silver metal, when it undergoes oxidation, becomes black in color, and the question says the metal oxide is reddish brown, so this option is incorrect. If we consider option C it says that copper, but we know that if copper is exposed to moist air it will form red copper oxide. While in case of option D, the aluminum upon exposure to air, forms white colored aluminum oxide, so option D would be incorrect.

So, the correct answer is Option A.

Additional information:
Ferric oxide, is the product that is formed when iron reacts with (\[{{H}_{2}}O+{{O}_{2}}\]) which means oxidation. This can be prepared in the laboratory by electrolyzing a sodium bicarbonate solution, an inert electrolyte, with an iron anode. The resulting hydrated Ferric oxide is dehydrated at around \[200{ }{}^\circ C\].

Ferric oxide (\[F{{e}_{2}}{{O}_{3}}\]) is used in paints and inks, plastics, rubber products and glass as a pigment. It is also used as a polishing agent for glass, diamonds and precious metals.

Note: When iron or any metal is exposed to moist air it undergoes the process of oxidation in order to form a layer of metal oxide. Those metal oxides of different metals have different colours. Iron in presence of moist air forms iron oxide, also called rust which is reddish-brown in colour. While in case of copper, silver and aluminum, the color of metal oxides are red, black and white.