Higher oxides of halogen tend to be more stable than lower one ...hence following that I guess decreasing order of oxidising power will be reverse. that is cl2o>clo2>cl2o6>cl2o7

Arrangement of Oxidising Power in Decreasing Order:

• Cl2O7


• Cl2O6


• Cl2O


• ClO2

Reasons for the Arrangement:

• Cl2O7: It has the highest oxidising power due to the presence of seven oxygen atoms, which makes it highly unstable and reactive. It can oxidise almost all elements except fluorine.


• Cl2O6: It has six oxygen atoms which makes it less reactive than Cl2O7, but still more reactive than Cl2O and ClO2.


• Cl2O: It has two oxygen atoms, and although it can oxidise some elements, its oxidising power is lower than Cl2O7 and Cl2O6.


• ClO2: It has only two oxygen atoms, and its oxidising power is the lowest of all the given compounds.

Explanation:
The oxidising power of a compound is determined by the number of oxygen atoms it contains. The more oxygen atoms, the higher the oxidising power. This is because oxygen is highly electronegative and attracts electrons towards itself, making it easier to remove electrons from other atoms and oxidise them.

Cl2O7 has the highest oxidising power because of the presence of seven oxygen atoms. It is highly unstable and reacts violently with almost all elements except fluorine. Cl2O6, with six oxygen atoms, is less reactive than Cl2O7 but still more reactive than Cl2O and ClO2. Cl2O has two oxygen atoms and can oxidise some elements, but its oxidising power is lower than Cl2O7 and Cl2O6. ClO2, with only two oxygen atoms, has the lowest oxidising power of all the given compounds.

Therefore, the given compounds can be arranged in decreasing order of oxidising power as Cl2O7 > Cl2O6 > Cl2O > ClO2.