Which condition condition must be true for a nation to exist

In order for a nation to exist the country must be sovereign and handle its own affairs.

A sovereign nation has one centralised government with the power to govern a defined geographic area.

A nation is defined as a common area inhabited by a group of people who share a language, culture, ethnicity, history and territory.

A sovereign nation has a permanent population, a government, in other words, it is not under the control of a foreign power: independence from other states; and  the capacity to enter into agreements and build relations with other sovereign states.

it's not the readmission

your answer would be (b)