Xavier
The proper noun is Jessica, the name of a person. A proper noun always starts with a capital letter.
David's
Nope. Common noun.
Ederlyn
eon, E. Coli, and ester
X-ray
xanadu
Proper nouns.
Yes, "Stefan" is a proper noun because it is a specific name for a person, place, or thing. It always starts with a capital letter.
No. The E in the proper adjective English has a short E sound. This is the same sound as in the proper noun England.
The word Exxon (capital E) is a proper noun, the name of a specific company. A proper noun is the name of a person, place, thing (a company), or a title. Always capitalize the first letter of a proper noun.