One of These is Not Like the Others

There is something similar about three of the entries in each set. Can you identify the odd one out?
None of these categories are numerical cutoffs
Remember, the three you don't select have to belong to a meaningful category.
Quiz by MiracleMax
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Last updated: May 10, 2020
First submittedMay 10, 2020
Times taken15
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1. Select the odd one out
Matterhorn
Puncak Jaya
Vinson Massif
Denali
Seven Summits
2. Select the odd one out
South Korea
United Kingdom
Indonesia
Gambia
One-Border Countries
3. Select the odd one out
Liechtenstein
Djibouti
Luxembourg
Singapore
Countries which share a name with their capital
4. Select the odd one out
South Africa
Belize
Thailand
Nigeria
Commonwealth Countries
5. Select the odd one out
Richard Wagner
Geronimo
Hideki Tojo
Ulysses S. Grant
Generals
6. Select the odd one out
Ozark Highlands
Everglades
Olympic
North Cascades
US National Parks
7. Select the odd one out
Monterrey
Jalisco
Tabasco
Sonora
Mexican States
8. Select the odd one out
Dead Sea
Great Salt Lake
Lake Titicaca
Salton Sea
Saltwater Lakes
9. Select the odd one out
Mumbai
Lima
London
Durban
Coastal Cities
10. Select the odd one out
Potato
Corn
Cranberry
Apple
Native to the Americas
11. Select the odd one out
St. Lawrence
Thames
Amazon
Ganges
Drain to the Atlantic
12. Select the odd one out
Cayenne
Toronto
Colorado Springs
Sydney
State/Province Capitals
+1
Level 81
May 10, 2020
Why isn't Lesotho the odd one out in 2, since it's the only land-locked one, Djibouti the odd one out in 3 since it's the only one with a low HDI, New Zealand the odd one out in 4 since it's the only island, the Everglades the odd one out in 6 since it's the only lowland region, Durban the odd one out in 9 since it's the only one one with an urban agglomeration population below 10 million, Potato the odd one out in 10 since it's the only one where the root is eaten, Thames the odd out in 11 since it has a discharge that is orders of magnitude smaller than the others, and Cayenne the odd one out in 12 since it's the only one where English is not the main language spoken?
+2
Level 71
May 10, 2020
I suspected I'd miss a few alternate sets. The Lesotho, New Zealand, and Cayenne questions have been fixed. I think arbitrary numberical cutoffs (for population, HDI, discharge) pretty clearly aren't insular categories, but I've noted that in a caveat. Also "lowland region" isn't meaningful. All of those places are in significantly different geological & ecological provinces. Also, Ozark Highlands isn't even a national park, making it the obvious choice.

Remember, it's not just picking the odd one out- the rest have to belong to a meaningful category. "plants where you don't eat the root" isn't really a cohesive category.