Balance the Half-Reaction, Cl₂O₇ $\rarr$ HClO, Taking Place in Acidic Media

Balance the half-reaction, Cl₂O₇ $\rarr$ HClO, taking place in acidic media. How many electrons are needed to balance the half-reaction?Hint: Remember the coefficients when balancing half-reactions and look carefully at the oxidation numbers.

A) 2 electrons, left side
B) 3 electrons, right side
C) 12 electrons, left side
D) 6 electrons, right side
E) 8 electrons, left side