Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction

Explanation

(a) Oxidation : The gain of oxygen by a substance in a reaction is called oxidation.
(i) When magnesium is burned in air then magnesium oxide is formed:
`underset("Magnesium")(2Mg)+underset("(From air)Oxygen")(O_(2))to underset("Magnesium oxide")(2MgO)`
In this reaction magnesium `(Mg)` has gained oxygen to form manesium oxide `(MgO)` so magnesium is oxidised to magnesium oxide.
(ii) When copper oxide is heated with hydrogen then copper metal and water and formed:
`underset("Copper oxide")(CuO) +underset("Hydrogen")(H_(2))to underset("Copper")(Cu)+underset("Water")(H_(2)O)`
In this case hydrogen `(H_(2))` is gainig oxygen to form water `(H_(2)O)` so hydrogen is getting oxidised to water.
(ii) Reduction: The loss of oxygen by a substance in a reaction is called reduction.
(i) When zinc oxide is heated with carbon, then zinc metal and carbon monoxide are formed:
`underset("Zinc oxide")(ZnO)+underset("Carbon")(C)to underset("Zinc")(Zn)+ underset("Carbon monoxide")(CO)`
In this reaction Zinc oxide `(ZnO)` is losing oxygen to form to form zinc metal `(Zn)` therefore zinc oxide is reduced to zinc.
(ii) When iron (III) oxide is heated with aluminium powder, then aluminium oxide and iron metal are formed:
`underset("Iron (III) oxide")(Fe_(2)O_(3))+underset("Aluminium")(2Al)to underset("Aluminium oxide")(Al_(2)O_(3))+underset("Iron")(2Fe)`
In this case iron (III) oxide `(Fe_(2)O_(3))` is losing oxygen to form metal `(Fe)`, therefore iron (III) oxide is reduced to iron.