An acidified solution of potassium chromate was layered with an equal volume of amyl alcohol. When it was shaken after the addition of $1 \mathrm{mL}$ of $3\% {\mathrm{H}}_2{\mathrm{O}}_2,$ a blue alcohol layer was obtained. The blue color is due to the formation of a chromium (VI) compound $\text{'}\mathrm{X}\text{'}$. What is the number of oxygen atoms bonded to chromium through only single bonds in a molecule of $\mathrm{X}$?

Hence, the correct answer is 4.