Q. The longest border between any two countries in the world is between:

• Canada and the United States of America
• Chile and Argentina
• China and India
• Kazakhstan and Russian Federation

Answer: (a) Canada and the United States of America.

Notes:

• Canada and the United States of America: The border between Canada and the United States is the longest international land boundary in the world, stretching over 8,890 kilometers (5,525 miles). This includes both the contiguous U.S.-Canada border and the boundary between Alaska and northern Canada.
• Chile and Argentina: This is the longest land border in South America, stretching along the Andes Mountains and running for about 6,691 kilometers (4,157 miles)​. While it’s long, it ranks third in the world after Canada–U.S. and Kazakhstan–Russia.
• China and India: The border between China and India is much shorter compared to other options, at about 3,488 kilometers (2,167 miles), making it far from the longest in the world​.
• Kazakhstan and Russian Federation: This is the second-longest international border, at approximately 7,644 kilometers (4,254 miles). Although significant, it’s still shorter than the Canada–U.S. border​.