An 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 $X$ ?

• A
  $2$
• B
  $3$
• C
  $4$
• D
  $5$