Yes, you should capitalize the C in Century.
nope, twenty-first century is fine
Yes. It should be----- Twenty-first Century Skills
No, except at the beginning of a sentence because it is not a proper noun.
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.
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.
Yes, "Twenty" and "Century" should be capitalized in "Twenty-first century" because they are considered proper nouns when referring to a specific time period.
In "Yours truly," you capitalize the first letter of each word if you are using it as a complimentary close in a letter, as it is a formal sign-off.
no, but you do capitalize mum
You capitalize the first A but not the last a.
You capitalize proper nouns.
No, you do not capitalize the word drama.