China has the most native speakers of Mandarin Chinese.
Mandarin is a group of related varieties within the Sinitic branch of the Sino-Tibetan language family. Standard Chinese, based largely on the Beijing dialect, is the official language of the People’s Republic of China and Taiwan, and one of Singapore’s official languages.
China’s enormous population makes it the clear country with the largest Mandarin-speaking population. Mandarin is also widely taught as a second language, so counts can differ depending on whether a source measures native speakers, total speakers, or speakers of Standard Chinese specifically.
Mandarin is often described as a single language, but the broader Mandarin group includes regional varieties that may sound very different from one another. It uses a tonal system, with Standard Chinese conventionally described as having four main tones plus a neutral tone. Cantonese is another major Chinese variety, but it is not Mandarin.