The acidic oxide among the following is:

The nature and characteristics of compounds determine the acidity of oxides. These binary oxides are created when other elements react with highly reactive oxygen. Metal oxides, which are basic, are created when metals and non-metals react with oxygen. Oxide is said to be acidic when it combines with water to form acid. Most non-metallic substances produce acidic oxides when they dissolve in water.

For example, silicon, phosphorus, sulphur, and chlorine oxides are acidic.

Non-metal reacts with oxygen to form acid-containing compounds combined with strong bonds. These compounds are also called acidic anhydride.

Now, the oxides of chorine are ${\mathrm{Cl}}_2\mathrm{O}$, ${\mathrm{ClO}}_2$, ${\mathrm{Cl}}_2{\mathrm{O}}_7$. Of all the chlorine oxides, dichloroheptoxide ${\mathrm{Cl}}_2{\mathrm{O}}_7$, Chlorine (VII) oxide has the highest acidity of all chlorine oxide. This is because it reacts with water, and forms a strong perchloric acid.

${\mathrm{Cl}}_2{\mathrm{O}}_7+{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{HClO}}_4$

Hence, the correct option is D.