Question: In what African country does the ethnicity form the largest ethnic group , for the ethnicity that has 3.5 million people total ?

text: List of ethnic groups of Africa
Lists -- Ethnic groups by region

The ethnic groups of Africa number in the thousands, with each population generally having its own language (or dialect of a language) and culture. The ethnolinguistic groups include various Afroasiatic, Khoisan, Niger-Congo and Nilo-Saharan populations. The official population count of the various ethnic groups in Africa is highly uncertain, both due to limited infrastructure to perform censuses and due to the rapid population growth. There have also been accusations of deliberate misreporting in order to give selected ethnicities numerical superiority (as in the case of Nigeria's Hausa, Fulani, Yoruba and Igbo people). A 2009 genetic clustering study, which genotyped 1327 polymorphic markers in various African populations, identified six ancestral clusters. The clustering corresponded closely with ethnicity, culture and language. A 2018 whole genome sequencing study of the world's populations observed similar clusters among the populations in Africa. At K=9, distinct ancestral components defined the Afrosiatic-speaking populations inhabiting North Africa and Northeast Africa; the Nilo-Saharan-speaking populations in Northeast Africa and East Africa; the Ari populations in Northeast Africa; the Niger-Congo-speaking populations in West-Central Africa, West Africa, East Africa and Southern Africa; the Pygmy populations in Central Africa; and the Khoisan populations in Southern Africa.
Name Family Language Region Country Population ( million )
Aka Nilo-Saharan , Pygmy Aka Central/Northern Western Central African Republic , Northwest Congo
Baka Pygmy Baka Central/Northern Western Equatoria in South Sudan 0.25
Banda Niger-Congo , Ubangian Banda language Chad Basin Central African Republic 1.5
Chewa Niger-Congo , Bantu Chichewa Central/Southern Botswana , Malawi , Mozambique , Namibia , Tanzania , Zambia , Zimbabwe 9
Chokwe Niger-Congo , Bantu Chokwe Central Angola , Congo ( Kinshasa ) , Zambia 1.1
Efé Nilo-Saharan , Pygmy Efe Central/Northern Ituri Rainforest of Congo
Gbaya Niger-Congo , Ubangian Gbaya language Chad Basin Central African Republic 1.5
Kongo Niger-Congo , Bantu Kongo Central Democratic Republic of the Congo , Angola , Republic of the Congo 10
Kanuri Nilo-Saharan , Western Saharan Kanuri Chad Basin Nigeria , Niger , Cameroon , Chad 10
Lingala Niger-Congo , Bantu Lingala Central Democratic Republic of the Congo , Republic of the Congo , Angola , Central African Republic
Luba Niger-Congo , Bantu Luba-Kasai , Luba-Katanga Central Democratic Republic of the Congo 13
Kotoko Afro-Asiatic , Chadic Lagwan Chad Basin Cameroon , Chad < 1
Mbunda Niger-Congo , Bantu Mbúùnda , Chimbúùnda , Mpuono Central Angola , Zambia 0.5
Mbundu Niger-Congo , Bantu Kimbundu Central Angola 2.4
Moghamo Niger-Congo , Southern Bantoid Moghamo Central/West Cameroon 0.018
Mongo Niger-Congo , Bantu Mongo Central Democratic Republic of the Congo 12
Ngamambo Niger-Congo , Southern Bantoid Ngamambo Central/West Cameroon 0.011
Ovimbundu Niger-Congo , Bantu Umbundu Central Angola 4.6
Sara Nilo-Saharan , Central Sudanic Sara Chad Basin Chad , Cameroon , Central African Republic 3.5
Sua Nilo-Saharan , Pygmy Sua Central/Northern Ituri Rainforest of Congo