Which of the metallic oxide can react with acids as well as bases? 

The metallic oxides that can react with acids and bases are known as amphoteric oxides. These compounds behave as bases when they react with acids and form normal salts.

These salts also behave as acids when they react with specific bases and form a complex salt as they cannot replace the metallic ion of the base.

Al₂O₃ being amphoteric in nature reacts with acids as well as bases to form salts.

${\mathrm{Al}}_2{\mathrm{O}}_3+ 6\mathrm{HCl}\to 2{\mathrm{AlCl}}_3+3{\mathrm{H}}_2\mathrm{O}$ (reaction with acid)

${\mathrm{Al}}_2{\mathrm{O}}_3+ 2\mathrm{NaOH}\to 2{\mathrm{NaAlO}}_2 + {\mathrm{H}}_2\mathrm{O}$(Reaction with a base). Here NaAlO₂ is a complex salt because aluminium being less reactive than sodium, cannot replace sodium from the base. Hence it combines with sodium to form a complex salt called sodium aluminate. 

On the other hand, Na₂O. CaO and FeO are pure basic oxides, and they only react with acids to form salt and water.