(a) Neutral oxides : CO Acidic oxides : $B_2O_3, SiO_2, CO_2$ Basic oxides : $Tl_2O_3$ Amphoteric oxides : $Al_2O_3, PbO_2$ (b) (i) CO Neutral to litmus [Neutral] (ii) $B_2O_3$ reacts with basic (metallic) oxides forming meta-borates. $B_2O_3 + CuO$ → $Cu(BO_2)_2$ [Acidic] (iii) $SiO_2 + 2NaOH$ → $Na_2SiO_3 + H_2O$ [Acidic] (iv) $CO_2 + 2NaOH$ → $Na_2CO_3 + H_2O$ [Acidic] (v) $Tl_2O_3 + 3H_2SO_4$ → $Tl_2(SO_4)_3 + 3H2_O$ [Basic] (vi) $Al_2O_3+6HCl$ → $2AlCl_3+3H_2O$ [Amphoteric] $Al_2O_3+2NaOH$ → $Na_2AlO_2+H_2O$ [Amphoteric] (vii) $PbO_2+2NaOH$ → $Na_2PbO_3+H_2O$ [Amphoteric] $PbO_2+4HCl$ → $PbCl_2+Cl_2+2H_2O$ [Amphoteric]