Contracted words.
"After school" is typically written as two words.
Chess player is written as two words.
"Pogostick" is typically written as one word.
"all day" is typically written as two separate words.
Hard work is written as two separate words.
"Fact sheet" is typically written as two words.
"Crash site" is typically written as two words.
One and two hundredths.
It is not one nor two words. It is hyphenated, just as it is written in the question.
Businessmen is often written as one word. It can be two words or even hyphenated
Underdeveloped should be written as one word, not two words or hyphenated. I hope this answered your question. :)
"Study hall" is typically written as two words.