Answer
$U + 2ClF_3 --> UF_6 + Cl_2$
Work Step by Step
1. Write the unbalanced equation
$U + ClF_3 --> UF_6 + Cl_2$
2. Balance the molecular equation:
*The number o U atoms in both sides are equal.(1)
*The number of Cl atoms in both sides aren't equal, add a 2 next to $ClF_3$, and that should fix that problem.
$U + 2 ClF_3 --> UF_6 + Cl_2$
*The number of F atoms in both sides are equal(6)
