The only nation bordering China, Russia, and South Korea is North Korea.
Mexico borders the US on the south and Canada on the north.
Russia.
Mexico.
Nigeria
Russia is the country that borders Finland on the east. Russia is the largest country in land mass in the world. It covers one eighth of the Earth.
That is Mongolia.
China and Russia border North Korea to the north while South Korea borders North Korea to the south. Russia's border with North Korea is on the far north east tip and is very small. China's border with North Korea is the largest of the North Korean borders.
Japan is an island nation without any borders.
The landlocked country that borders China to the south and Russia to the north is Mongolia. The capital of Mongolia is Ulan Bator.
North Korea is the only nation to border both China and South Korea.
Brazil borders all but two of the countries in South America.