Answer
Please see the work below.
Work Step by Step
We know that
$\frac{u_{H_2}}{u_{I_2}}=(\frac{M_m(I_2)}{M_m(H_2)})^{\frac{1}{2}}$
We plug in the known values to obtain:
$\frac{u_{H_2}}{u_{I_2}}=(\frac{253.8}{2.016})^\frac{1}{2}=11.22$
Now $t(H_2)=39\times \frac{1}{11.22}=3.47s$