in 1900's or in the 1900's
in 1900's or in the 1900's?

in early 19th century or in the early 19th century?

in early 1900 or in the early 1900?

Please help me, thank you!

Question

in 1900's or in the 1900's 
in 1900's or in the 1900's?

in early 19th century or in the early 19th century?

in early 1900 or in the early 1900?

Please help me, thank you!

Answer

I agree with Norman on all counts, but would add that the apostrophe in "1900's" is unnecessary.

The apostrophe is used in making plurals where the meaning would otherwise be unclear. Example: "How many a's are there in "language"?" would  be unclear without the apostrophe.

There is no such uncertainty in "1900s", so it's not needed.

Answer

Hi Durk,

in the 1900's

in the early 19th century

in early 1900