Tellurium dioxide is a solid oxide

Oxide

An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

 of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite

Tellurite

Tellurite is a rare oxide mineral composed of tellurium dioxide .It occurs as prismatic to acicular transparent yellow to white orthorhombic crystals. It occurs in the oxidation zone of mineral deposits in association with native tellurium, emmonsite and other tellurium minerals. Its name comes...

, β-TeO₂, and the synthetic, colourless tetragonal (paratellurite), α-TeO₂. Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO₂.
Paratellurite, α-TeO₂, is produced by reacting tellurium with O₂:

Te + O₂ → TeO₂

An alternative preparation is to dehydrate tellurous acid, H₂TeO₃, or to thermally decompose basic tellurium nitrate,Te₂O₄.HNO₃ above 400°C.
TeO₂ is highly insoluble in water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and soluble in concentrated sulfuric acid

Sulfuric acid

Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

.
It is also incompatible with strong acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

s and strong oxidizing agent

Oxidizing agent

An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...

s.