To answer this question, the user needs to have knowledge of the history of Bangalore and the occurrence of plagues.

Option A: 1798 - This is not the correct answer. There is no record of a plague outbreak in Bangalore in 1798.

Option B: 1788 - This is not the correct answer. There is no record of a plague outbreak in Bangalore in 1788.

Option C: 1898 - This is the correct answer. In 1898, Bangalore was hit by a plague outbreak, which reduced its population dramatically.

Option D: 1888 - This is not the correct answer. There is no record of a plague outbreak in Bangalore in 1888.

Therefore, the answer is: C. 1898.