In the following sentence, four words printed in bold are given. One of these words printed in bold might either be wrongly spelt or inappropriate to the context of the sentence. Find out that word that is inappropriate or wrongly spelt, if any. If all of the words in bold are correct, then mark 'No error' as your answer.

The glass transition is the gradual and reversible transition in amorphous materials from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased.