Is this the 21'st century? ?

Question

A century is 100 years, so than the 1900's were the 20'th century and the 1800's were the 19'th century?

Is this correct?

What was 1000 Common Era? Was that the 1'st century? Because that is a thousand years, not a hundred.

What was 900 C.E.?

Answer 1

common era was 11 century and in this moment is 21 century...

Answer 2

Correct.

Answer 3

This appears to be indeed the 21st Century, and you are correct about the others (1900s and 1800s). The Common Era is not a century, the word "era" does not define a certain number of years rather a period in history. It could be any number of years in length, from a couple to thousands, because it is defined by one or more certain events. Not sure about 900 C.E. but the link I'm providing is bound to give you answer.