  The quantum Hall effect is observed in a two-dimensional electron gas formed
in millimeter-scale hydrogenated graphene, with a mobility less than 10
$\mathrm{cm^{2}/V\cdot s}$ and corresponding Ioffe-Regel disorder parameter
$(k_{F}\lambda)^{-1}\gg1$. In zero magnetic field and low temperatures, the
hydrogenated graphene is insulating with a two-point resistance of order of
$250 h/e^2$. Application of a strong magnetic field generates a negative
colossal magnetoresistance, with the two-point resistance saturating within
0.5% of $h/2e^{2}$ at 45T. Our observations are consistent with the opening of
an impurity-induced gap in the density of states of graphene. The interplay
between electron localization by defect scattering and magnetic confinement in
two-dimensional atomic crystals is discussed.
