Which of the following novels is NOT written by Amitav Ghosh?

The correct option is English, August.

To understand why this is the correct answer, we can look at the authors of each of the novels listed in the options:
1. Sea of Poppies: This novel, published in 2008, was written by Amitav Ghosh. It is the first book of his acclaimed Ibis Trilogy, which is set in the 1830s just before the First Opium War.
2. Flood of Fire: This novel, published in 2015, was also written by Amitav Ghosh. It serves as the third and final volume of the Ibis Trilogy.
3. Gun Island: This novel, published in 2019, is a work by Amitav Ghosh that explores themes of climate change, migration, and mythology.
4. English, August: Published in 1988, this sub-titled novel ("An Indian Story") is a famous satirical work written by the Indian author Upamanyu Chatterjee, depicting the life of a young IAS officer posted in a remote Indian town.

Since English, August was written by Upamanyu Chatterjee, it is the only novel in the list that was NOT written by Amitav Ghosh.