The Ghadr (Ghadar) was a

1. The Ghadr (or Ghadar) Party was primarily a revolutionary association of Indians, mainly Sikhs from Punjab, established abroad with the aim of overthrowing British rule in India. 2. Its formation was formalized in 1913, and its headquarters were established at San Francisco, USA. The party published a weekly newspaper called 'Ghadr'. 3. Option (A) correctly identifies it as a revolutionary association with headquarters at San Francisco. 4. Option (B) is incorrect; while there were nationalist activities in Singapore, the Ghadar party's main base was North America. 5. Option (C) is incorrect; while Indian revolutionaries operated from Berlin (e.g., Berlin Committee during WWI), it was not the headquarters of the Ghadar party. 6. Option (D) is incorrect; the Ghadar movement was primarily nationalist and revolutionary, not explicitly communist in its core ideology at inception. Early communist activities related to India were centered in places like Tashkent later, but that's distinct from the Ghadar party's origins and main base.