Which of the following oxides is amphoteric in character?

The correct option is SnO₂.

To understand why tin dioxide (${\mathrm{SnO}}_2$) is amphoteric, let's break down the nature of oxides based on the position of their elements in the periodic table:
1. Amphoteric Oxides: These are oxides that can react with both acids and bases to form salts and water. Elements that form amphoteric oxides are usually metalloids or metals near the border between metals and non-metals (such as aluminium, zinc, lead, and tin).
2. Acidic Oxides: These are oxides of non-metals (like carbon and silicon) that react with bases to form salts. Carbon dioxide (${\mathrm{CO}}_2$) and silicon dioxide (${\mathrm{SiO}}_2$) are acidic oxides.
3. Basic Oxides: These are oxides of highly electropositive metals (like calcium) that react with acids to form salts. Calcium oxide ($\mathrm{CaO}$) is a strongly basic oxide.

Tin ($\mathrm{Sn}$) is a Group 14 post-transition metal. Due to its intermediate metallic character, its oxide, tin dioxide (${\mathrm{SnO}}_2$), exhibits both acidic and basic properties.

We can demonstrate the amphoteric behavior of ${\mathrm{SnO}}_2$ through its reactions with a strong acid and a strong base:

Reaction with a strong acid (acting as a base):
When tin dioxide reacts with concentrated hydrochloric acid, it forms tin(IV) chloride and water:
${\mathrm{SnO}}_2+4\mathrm{HCl}\to {\mathrm{SnCl}}_4+2H_{2}O$

Reaction with a strong base (acting as an acid):
When tin dioxide reacts with concentrated sodium hydroxide, it forms sodium stannate and water:
${\mathrm{SnO}}_2+2\mathrm{NaOH}+2H_{2}O\to {\mathrm{Na}}_2\left[\mathrm{Sn}{\left(\mathrm{OH}\right)}_6\right]$
(or simplified as ${\mathrm{SnO}}_2+2\mathrm{NaOH}\to {\mathrm{Na}}_2{\mathrm{SnO}}_3+H_{2}O$).

Therefore, because ${\mathrm{SnO}}_2$ reacts with both acids and bases, it is classified as amphoteric in character.