Take a look at the database structure for cities in nations below. There are numerous cities in a nation, and the same city name can be found in several countries. Country (integer ID, string (unique)...

Take a look at the database structure for cities in nations below. There are numerous cities in a nation, and the same city name can be found in several countries.

Country (integer ID, string (unique) name)

(serialNo: integer (not null), CountryID: integer, CityName: string, Population: integer)

Is it possible for a city to have an unknown CityName?

No, it's against the rules of the domain.

Yes.

No, infringe.