When was Bangladesh formed as a country?

1971

The correct answer is Option 3 - 1971

In Bengal the migration was even more protracted, with people moving across a porous border. This also meant that the Bengali division produced a process of suffering that may have been less concentrated but was as agonising. Furthermore, unlike the Punjab, the exchange of population in Bengal was not near-total. Many Bengali Hindus remained in East Pakistan while many Bengali Muslims continued to live in West Bengal. Finally, Bengali Muslims (East Pakistanis) rejected Jinnah’s two-nation theory through political action, breaking away from Pakistan and creating Bangladesh in 1971-72. A common religion could not hold East and West Pakistan together.