1. List the given oxides

We need to count how many of the following are amphoteric:

$\mathrm{Cl_2O_7,\ CO,\ PbO_2,\ N_2O,\ NO,\ Al_2O_3,\ SiO_2,\ N_2O_5,\ SnO_2}$

An amphoteric oxide is one that reacts with both acids and bases.

2. Check each oxide one by one

(i) $\mathrm{Cl_2O_7}$

This is the anhydride of perchloric acid:

$\mathrm{Cl_2O_7 + H_2O \rightarrow 2HClO_4}$

So it is an acidic oxide, not amphoteric.

(ii) $\mathrm{CO}$

Carbon monoxide is a neutral oxide. It is neither acidic nor basic. So, not amphoteric.

(iii) $\mathrm{PbO_2}$

Lead dioxide shows amphoteric character. It reacts with acids and also with strong bases. Hence, amphoteric.

(iv) $\mathrm{N_2O}$

Nitrous oxide is a neutral oxide. So, not amphoteric.

(v) $\mathrm{NO}$

Nitric oxide is also a neutral oxide. So, not amphoteric.

(vi) $\mathrm{Al_2O_3}$

Aluminium oxide is a standard example of an amphoteric oxide. It reacts with both acids and bases. Hence, amphoteric.

(vii) $\mathrm{SiO_2}$

Silicon dioxide is an acidic oxide. It reacts with bases, not with acids in the amphoteric sense. So, not amphoteric.

(viii) $\mathrm{N_2O_5}$

This is the anhydride of nitric acid:

$\mathrm{N_2O_5 + H_2O \rightarrow 2HNO_3}$

So it is an acidic oxide, not amphoteric.

(ix) $\mathrm{SnO_2}$

Tin dioxide is amphoteric. It reacts with both acids and bases. Hence, amphoteric.

3. Count the amphoteric oxides

The amphoteric oxides are:

$\mathrm{PbO_2,\ Al_2O_3,\ SnO_2}$

Number of amphoteric oxides:

$3$

4. Compare with stored answer

Stored correct answer = $3$

Our derived answer = $3$

So they agree.