The oxides of group 13 elements are given as 

a) ${\mathrm{B}}_2{\mathrm{O}}_3$ 

b) ${\mathrm{Al}}_2{\mathrm{O}}_3$ 

c) ${\mathrm{Ga}}_2{\mathrm{O}}_3$ 

d) ${\mathrm{In}}_2{\mathrm{O}}_3$

a and b are basic in nature

c and d are acidic in nature

a and d are neutral

b and c are amphoteric in nature