Option 1: October 2016 -> This is before the actual demonetization announcement.
Option 2: September 2016 -> This is two months before the actual event.
Option 3: December 2016 -> This is after the demonetization was announced and implemented.
Option 4: November 2016 -> This is when the demonetization was announced.
Hence, Option 4: November 2016 -> The Government of India announced the demonetization of Rs 500 and Rs 1000 currency notes on November 8, 2016. Prime Minister Narendra Modi made this historic announcement in a televised address to the nation at 8 PM, declaring that these notes would cease to be legal tender from midnight of the same day. This was done primarily to curb black money, counterfeit currency, and corruption. -> correct