“Turn of the century” refers to the transition from one century to another. The turn of the century discussed in your lectures refers to the transition from the 1800s to the 1900s.

The statement is true on turn of the century

Explanation:

Turn of the century refers to the transition from one century to another". The term is  used to indicate a distinct Period of Time either before/after the beginning of a centuryor both before & after

For instance, 'the turn of the 19th century' refers to the years immediately preceding and immediately following 1801, 'the turn of the 19th century' to the years surrounding 1801, and so on.

Or

For instance, if a statement describes an event as taking place "at the turn of the 19th century," it could refer to a period around the year 1801 or around 1900, that is, the beginning or end of that century.