The changes which take place rapidly are called fast changes. The changes which take place slowly are called slow changes. Slow and fast changes are relative to each other.
Among the given options, growing of tree is the slowest change as it takes many years. The curdling of milk takes 24 hours. The boiling of milk takes few minutes. The glowing of bulb happens rapidly as compared to other given changes. So, the correct sequence of the given changes from slowest to fastest is:
Growing of tree < Curdling of milk < Boiling of milk < Glowing of bulb