Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
The following is a list of mountains that have been presumed, at one time, to be the highest mountain in the world. How general the following presumptions were is unclear. Before the Age of Discovery, no geographer could make any plausible assumption.
Chimborazo, 6,267 metres (20,561 ft). Presumed highest from sixteenth century until the beginning of the 19th century. Not in the top 100 highest mountains when measured from sea level, however due to the Earth's equatorial bulge this is the farthest point from the Earth's center.
Nanda Devi, 7,816 metres (25,643 ft). Presumed highest in the world in an era when Nepal was still closed to the outside world. Now known to be the 23rd highest mountain in the world.
Dhaulagiri, 8,167 metres (26,795 ft). Presumed highest from 1808 until 1847. Now known to be the 7th highest mountain in the world.
Kangchenjunga, 8,586 metres (28,169 ft). Presumed highest from 1847 until 1852. Now known to be the 3rd highest mountain in the world.
K2, 8,611 metres (28,251 ft). Discovered in 1856 before Mount Everest's status was officially confirmed, K2's elevation became something of an enigma until it was officially resolved at a later date. News media reported in 1986 that satellite measurements by the University of Washington during an expedition to K2 by George Wallenstein had given a height between 29,064 feet (8,859 m) and 29,228 feet (8,909 m), which would have made it the world's highest mountain. However, this erroneous figure was quickly retracted, and K2's status as second highest was reaffirmed.
Mount Everest, 8,849 metres (29,032 ft). Established as highest in 1852 and officially confirmed in 1856.