Final answer:
Japan is the East Asian country that can only use around 12 percent of its land for farming due to its mountainous terrain.
Step-by-step explanation:
The country in East Asia that can only use 12 percent of its land for farming is Japan. Japan is a mountainous archipelago where flat land is scarce, leading to a significant limitation in arable land availability for agriculture. Due to its geographic and topographic challenges, Japan has developed intensive agricultural techniques to maximize the use of available land. However, this still results in a limited percentage of land that is suitable for farming, emphasizing the need for high efficiency in agricultural practices to support its population.