Mexico
The southern tip of South America is closer to Antarctica and the South Pole than Australia.
The tip of south America closest to Antarctica is Argentina.
South America is a continent, not a single country. It is made up of 15 separate countries. If by America you mean the United States, the country closest to the south of the United States is Mexico.
Spain, not england.
England
Mexico is the closest country south of the US, as it borders the US to the south.
The three continents closest to Antarctica are South America, Australia, and Africa. South America is the closest, with the tip of the Antarctic Peninsula being only about 1,000 kilometers away from the southernmost point of South America. Australia is next, with the closest point being around 2,200 kilometers away from Antarctica. Africa is the third closest continent to Antarctica, with the closest point being approximately 4,000 kilometers away.
South America
It's closer to South America, but politically the Caribbean is usually treated as part of North America, so Trinidad and Tobago is a North American country.
Australia is closer (South America is closest of all). Also, note that Australia is not a continent. This means the closest continent to the South Pole is South America.
The country is England and the capital is London.