Perhaps Nigeria but I feel like it would still be one of the countries named first if people had to name african countries (after egypt & south africa maybe).
Tanzania on 24, Myanmar on 26 (!), Uganda on 32, maybe Sudan on 35, Uzbekistan on 39, Angola on 42 and Mozambique on 45 are good candidates. Perhaps Yemen, Ghana & Ivory Coast but i feel like all of these have a bit more name recognition.
Out of the top 50, i bet the least named country would be Myanmar, Angola or Mozambique out of these. Maybe Uzbekistan and Tanzania. And that would almost certainly be the top five.
Some African nations would simply be more known to ppl in Europe because they would have a great football team like Ivory Coast, Nigeria, Senegal, Ghana & Cameroon.
So for that reason, Angola has a decent team but it's been a while - since 2006 - they have been on a tournmaent, so i guess Myanmar or Mozambique would be the answer. The first at least has some coverage because of political events (the junta & Aung but that'll only be highly informed people), but I rarely like ever hear abouT Mozambique... and if i never heard it was a country, it would be the most likely one to not have heard off.
So i bet its Mozambique.
Outside of Lusophone countries I suspect Mozambique is extremely anonymous.