Which statement about the glass transition temperature Tg when a glass is cooled from the melt is correct?

Answer: C. The faster the cooling rate, the higher Tg

As a melt cools, its viscosity rises steeply, and at the temperature where atomic rearrangement can no longer keep up with cooling, the structure freezes in and the slope of specific volume versus temperature changes. This temperature is the glass transition temperature Tg, at a viscosity of roughly 10¹² Pa·s. The faster the cooling, the less time atoms have to rearrange, so the structure freezes in at a higher temperature and Tg is higher; the frozen-in structure is then a lower-density state. Tg is not the temperature of a thermodynamic phase transition like a melting point, so it is not fixed independent of cooling rate. This property also bears on removing residual stresses by annealing glass.