It is capitalized at the beginning of the sentence or when it forms part of the proper noun.
Examples:
The 2nd century is considered part of the Classical era.
The Second Century Initiative is celebrating its anniversary.
No, it shouldn't be capitalized.
In the middle of a sentence, you don't capitalize second floor.
Yes. It should be----- Twenty-first Century Skills
No. Use italics if possible or underline and capitalize the genus (first word) but not the second (species). E.g. Alces alces
No it shouldn't be capitalized.
You don't use caps with it because it isn't a proper noun. If you wrote Mrs. Smith's second grade it still wouldn't have caps.
Yes, you should capitalize the C in Century.
Yes you do
No, you do not capitalize the second word in the complimentary closing.
In the middle of a sentence, you don't capitalize second floor.
nope, twenty-first century is fine
Yes. It should be----- Twenty-first Century Skills
No
No. Use italics if possible or underline and capitalize the genus (first word) but not the second (species). E.g. Alces alces
When you are naming a Century, capitalize it: Ireland was a beacon of civilization in the Fourth Century. When you are referring to the passage of time, do not: In this fourth century of her history, let us help our Country keep the promises of freedom and justice made in the first three.
No. It's not necessary.
In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.In the second century under the rule of Trajan.
No it shouldn't be capitalized.