Question

Which of the following is an amphoteric oxide?
A. \[{{MgO}}\]
B. ${{A}}{{{l}}_2}{{{O}}_3}$
C. ${{Si}}{{{O}}_2}$
D. ${{{P}}_2}{{{O}}_5}$

Answer 1

Hint:When an element reacts with oxygen, it forms oxides. Amphoteric oxides are generally oxides of metal. We can determine the amphoteric oxides from the given options by checking whether the options are metal oxides or not. But basic oxides are also metal oxides.

Complete step by step answer:
Oxides are of four types-acidic, basic, neutral and amphoteric oxides. Acidic oxides are generally non-metal oxides. We shall know why it is known as acidic oxides. Acids are formed when acidic oxides react with water.
E.g. ${{S}}{{{O}}_3} + {{{H}}_2}{{O}} \to {{{H}}_2}{{S}}{{{O}}_4}$
Here, sulfur trioxide reacts with water to give sulfuric acid which is a strong acid.
While basic oxides are generally metal oxides. Bases are formed when basic oxides react with acids. Mostly, they do not dissolve in water.
E.g. ${{N}}{{{a}}_2}{{O}} + {{HCl}} \to {{NaOH}} + {{{H}}_2}{{O}}$
This reaction is typically a neutralization reaction.
Neutral oxides do not have acidic or basic properties.
When amphoteric oxides are reacted with acids and bases, it gives salt.
In the given options, ${{A}}{{{l}}_2}{{{O}}_3}$ acts as an amphoteric oxide. The reaction of ${{A}}{{{l}}_2}{{{O}}_3}$ with acids and bases is given below:
${{A}}{{{l}}_2}{{{O}}_3} + {{HCl}} \to {{AlC}}{{{l}}_3} + {{{H}}_2}{{O}}$
  ${{A}}{{{l}}_2}{{{O}}_3} + {{NaOH}} \to {{N}}{{{a}}_2}{{A}}{{{l}}_2}{{{O}}_4} + {{{H}}_2}{{O}}$
 Thus we can say that ${{A}}{{{l}}_2}{{{O}}_3}$ is an amphoteric oxide. \[{{MgO}}\] is a basic oxide. ${{Si}}{{{O}}_2}$ does not have any reaction with water. Thus its acidic or basic character cannot be determined. ${{{P}}_2}{{{O}}_5}$ is acidic in nature.

Hence, the correct option is B.

Note:
On moving down the group, oxides vary differently. In p-block, the acidic character of oxides decreases on moving down the column. While on moving from left to right, acidic character is more on right and basic character is on the left side.