Is this by total speakers or native speakers? If it is by total, Malay should be the most spoken of the Austronesian, as most Indonesians learn it as a second language (referred to as Bahasa Indonesia), for a total of 200-250 million speakers. If it's by native speakers, then Spanish and Yoruba should be the leaders in Indo-European and Niger-Congo, respectively.
A nice quiz, but what stands for 'Caucasian' language family? There is a (hypothetical) family called North Caucasian, but Georgian is by no means related to it. It's a completely different family, Kartvelian. I think this should be fixed somehow.