Classify following oxides as neutral, acidic, basic or amphoteric:

(1) CO = Neutral

(2) $\mathrm{B}_{2} \mathrm{O}_{3}=$ Acidic

Being acidic, it reacts with bases to form salts. It reacts with NaOH to form sodium metaborate.

$\mathrm{B}_{2} \mathrm{O}_{3}+2 \mathrm{NaOH} \longrightarrow 2 \mathrm{NaBO}_{2}+\mathrm{H}_{2} \mathrm{O}$

(3) $\mathrm{SiO}_{2}=$ Acidic

Being acidic, it reacts with bases to form salts. It reacts with NaOH to form sodium silicate.

$\mathrm{SiO}_{2}+2 \mathrm{NaOH} \longrightarrow 2 \mathrm{Na}_{2} \mathrm{SiO}_{3}+\mathrm{H}_{2} \mathrm{O}$

(4) $\mathrm{CO}_{2}=$ Acidic

Being acidic, it reacts with bases to form salts. It reacts with NaOH to form sodium carbonate.

$\mathrm{CO}_{2}+2 \mathrm{NaOH} \longrightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} \mathrm{O}$

(5) $\mathrm{Al}_{2} \mathrm{O}_{3}=$ Amphoteric

Amphoteric substances react with both acids and bases. $\mathrm{Al}_{2} \mathrm{O}_{3}$ reacts with both $\mathrm{NaOH}$ and $\mathrm{H}_{2} \mathrm{SO}_{4}$.

$\mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{NaOH} \longrightarrow \mathrm{NaAlO}_{2}$

$\mathrm{Al}_{2} \mathrm{O}_{3}+3 \mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}+3 \mathrm{H}_{2} \mathrm{O}$

(6) $\mathrm{PbO}_{2}=$ Amphoteric

Amphoteric substances react with both acids and bases. $\mathrm{PbO}_{2}$ reacts with both $\mathrm{NaOH}$ and $\mathrm{H}_{2} \mathrm{SO}_{4}$.

$\mathrm{PbO}_{2}+2 \mathrm{NaOH} \longrightarrow \mathrm{Na}_{2} \mathrm{PbO}_{3}+\mathrm{H}_{2} \mathrm{O}$

$2 \mathrm{PbO}_{2}+2 \mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow 2 \mathrm{PbSO}_{4}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$

(7) $\mathrm{Tl}_{2} \mathrm{O}_{3}=$ Basic

Being basic, it reacts with acids to form salts. It reacts with HCl to form thallium chloride.

$\mathrm{Tl}_{2} \mathrm{O}_{3}+6 \mathrm{HCl} \longrightarrow 2 \mathrm{TICl}_{3}+3 \mathrm{H}_{2} \mathrm{O}$