A flask of O2(g) is heated from 10 C to 90 C. are all the O2 molecules moving faster at 90 C?

Technically, no. The average kinetic energy of the gas sample increases with temperature, meaning that, on average, the speed of all the particles increases. However, the Maxwell–Boltzmann distribution of velocities ranges from 0 (no motion of a gas molecule) to some maximum related to temperature. Since it is likely that a infinitesimal fraction of the molecules are not moving at any given time, it is technically incorrect to say all molecules are moving faster at the higher temperature, as there will always be a few that are not moving at all at both temps.