Question

Which one of the following is an amphoteric oxide?
A. $Sr{{\left( OH \right)}_{2}}$
B. $Ca{{\left( OH \right)}_{2}}$
C. $Mg{{\left( OH \right)}_{2}}$
D. $Be{{\left( OH \right)}_{2}}$

Answer 1

Complete step by step solution:
-Oxides are the compounds which contain the bond between an element and oxygen atom. They
are of four types, basic, acidic, neutral and amphoteric oxides.
-The basic oxides give $O{{H}^{-}}$ ions when they are dissolved in water. The acidic oxides
give ${{H}^{+}}$ ions when dissolved in water. Neutral oxides are those which do not give any
ion on dissolution in water while the amphoteric oxides give both the ions when they are
dissolved in water.
-To know about the nature of oxides, we need to know the element forming the oxides. A non-
metal can make 2 types of oxides, neutral and acidic oxides. Only the oxides of $CO$, $NO$ and ${{N}_{2}}O$ are the neutral oxides of non-metals and all the rest are acidic oxides.
-Amphoteric oxides can be formed by metals as well as by the metalloids. The metals which
have the oxidation state of +4 always form the amphoteric oxides. The other metals which can
form amphoteric oxides in all the oxidation states are $Zn$, $Be$, $Al$, $Cr$, $V$, $Ga$ and $Pb$.
-All the other metals form basic oxides only if they are not in their +4 oxidation states. The
metalloids can also form amphoteric oxides along with acidic oxides. The metalloids of Sb and
As form the amphoteric oxides.
-In the question we see that all the elements are in +2 oxidation state and all the elements given
are metals. Among them, Be is the only metal which forms amphoteric oxide in all its oxidation
states.

Therefore the correct option is D.

Note: Metals can form acidic, basic and amphoteric oxides. The acidic nature of the oxides increases with the increase in the oxidation state. Only +4 oxidation state yields amphoteric
oxide. The oxidation states of +1,+2,+3 yield basic oxides and that of +5,+6,+7 yield acidic
oxides.