In which year was the "One Nation One FASTag" scheme implemented?

The correct answer is Option (2) → 1 December 2019

FASTag is a sticker with an RFID chip fixed on a vehicle’s windscreen; the toll is cut from a linked prepaid or bank account as the vehicle drives through, without stopping at the toll plaza. Under “One Nation One FASTag” a single tag works at toll plazas all over the country. The Ministry of Road Transport and Highways notified that all lanes of toll plazas on national highways would become FASTag lanes from 1 December 2019, so the scheme came into force in 2019.