A n acidified solution of potassium chromate was layered with an equal volume of amyl alcohol. When it was shaken after the addition of 1 mL of 3% $$H_2O_2$$, a blue alcohol layer was obtained. The blue color is due to the formation of a chromium (VI) compound ‘X’. What is the number of oxygen atoms bonded to chromium through only single bonds in a molecule of X?

Potassium chromate in acidic medium first converts to dichromate, which then reacts with hydrogen peroxide to give a blue peroxo-compound of chromium(VI):

$$Cr_2O_7^{2-} + 4\,H_2O_2 + 2\,H^+ \;\longrightarrow\; 2\,CrO_5 + 5\,H_2O$$

The compound extracted into the amyl-alcohol layer is $$CrO_5$$ (commonly written as $$O = Cr(O_2)_2$$). Its structure is:

$$\displaystyle O = Cr\bigl(O{-}O\bigr)_2$$

Explanation of the structure:
• One oxygen atom forms a double bond with chromium (the oxo group $$Cr{=}O$$).
• Two peroxide groups $$(O{-}O)$$ are each attached to chromium through a single $$Cr{-}O$$ bond.   Each peroxide ligand contains two oxygen atoms, so there are $$2 \times 2 = 4$$ oxygen atoms involved in single bonds to chromium.

Therefore, the number of oxygen atoms bonded to chromium exclusively through single bonds is

$$4$$

Final Answer: 4