China's Chairman Mao Zedong is primarily known for b) creating the People's Republic of China and implementing the Cultural Revolution.
While he played a significant role in the communist victory during the Chinese Civil War and was involved in the war against Japan, his most notable contributions are the establishment of the People's Republic of China in 1949 and for spearheading the Cultural Revolution (1966-1976), which aimed to reinforce communist ideology by purging remnants of capitalist and traditional elements from Chinese society.
Options a, c, and d involve inaccuracies regarding Mao's role or refer to events that occurred after his significant periods of leadership. For example, modernizing China's economy in the 1970s and 80s is more associated with Deng Xiaoping, who succeeded Mao. Additionally, while Mao's policies did lead to significant societal upheaval, his direct encouragement regarding the Tiananmen Square protests does not align with historical events since those occurred long after his death in 1976.