The blue colour is produced on adding H₂O₂ in acidified K₂Cr₂O₇ solution is due to the formation of which of the following?

CrO₅

The reaction between acidified K₂​Cr₂​O₇​ and H_2​O₂​ is given as:

K₂​Cr₂​O₇ + 4H_2​O₂ + H₂SO₄ → 2CrO₅ + K₂SO₄ + 5H₂O 

The deep blue colour obtained is due to formation of CrO5​; which fades away and compound gets decomposed  to Cr³⁺ and O₂(g) in the aqueous solution readily. So, ether is added to extract CrO₅​ because it will remain stable in such medium.