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Which of the following oxides is not expected to react with sodium hydroxide?
A
BeO
B
$B_2O_3$
C
CaO
D
$SiO_2$
Detailed Solution
Sodium hydroxide is a base; it reacts with acidic and amphoteric oxides but not with basic oxides.
BeO is amphoteric: $BeO + 2NaOH \rightarrow Na_2BeO_2 + H_2O$
$B_2O_3$ is acidic: $B_2O_3 + 6NaOH \rightarrow 2Na_3BO_3 + 3H_2O$
$SiO_2$ is acidic: $SiO_2 + 2NaOH \rightarrow Na_2SiO_3 + H_2O$
CaO is a basic oxide, so it does not react with another base.
Hence CaO is not expected to react with sodium hydroxide.
BeO is amphoteric: $BeO + 2NaOH \rightarrow Na_2BeO_2 + H_2O$
$B_2O_3$ is acidic: $B_2O_3 + 6NaOH \rightarrow 2Na_3BO_3 + 3H_2O$
$SiO_2$ is acidic: $SiO_2 + 2NaOH \rightarrow Na_2SiO_3 + H_2O$
CaO is a basic oxide, so it does not react with another base.
Hence CaO is not expected to react with sodium hydroxide.