Please answer Q18 and tell why the other options are incorrect.

Dear Student,
Al₂O₃ is amphoteric oxide. 
Al₂O₃ + 6HCl $\stackrel{}{\to }$ 2AlCl₃ + 3H₂O
Al₂O₃ + 2NaOH $\stackrel{}{\to }$ 2NaAlO₂ + H₂O
Since Al₂O₃ reacts with both acid and base, hence it is an amphoteric oxide

Regards