Question

Which of the following are amphoteric oxides?
A. $CaO$
B. $NaOH$
C. $BeO$
D. $LiOH$

Answer 1

Hint: Oxides that react with both acids as well as base and produce salts and water are called amphoteric oxides. Most metals form the amphoteric oxides. “amphoteric” the prefix of the word was derived from the prefix of the word was derived from Amphi (that means both). Amphoterism also depends upon the oxidation states of oxide.

Complete answer:
A. Calcium oxide is not an amphoteric oxide rather $CaO$ is a basic oxide and when it reacts with acid, salt and water are produced.
$CaO + 2HCl \to CaC{l_2} + {H_2}O$
Calcium oxide on reaction with water produces calcium hydroxide which is a basic solution.
B. Sodium is an alkali metal. On moving from left to right the electronegativity increases and in NaOH there is a large electronegativity difference and this is one of the reasons why $NaOH$ behaves as a base.
C. $BeO$ is amphoteric as BeO reacts with acid as well as a base.
$BeO$ on reaction with sodium hydroxide (base) yields a sodium beryllate salt and water. In this case, $BeO$ acts as an acid.
$BeO + 2NaOH \to N{a_2}Be{O_2} + {H_2}O$
When BeO reacts with hydrochloric acid, barium chloride and water is produced.
$BeO + 2HCl \to BeC{l_2} + {H_2}O$
D. $LiOH$ is not an amphoteric oxide. $LiOH$ is a strong base. $L{i^ + }$ and $O{H^ - }$ ions are formed on complete dissociation of $LiOH$ in aqueous solution.
Therefore the correct answer is option C.

Note:
Metal and oxygen together form metallic oxides and it is formed by oxidation of metals. Non-Metallic oxides are made of non-metal and oxygen and it is formed on oxidation of non-metals. Some of the examples of metallic oxides are $FeO,A{l_2}{O_3},N{a_2}O$ and non-metallic oxides are $N{O_2},CO$.