The proper adjective for Persia is spelled "Persian." This term is used to describe anything related to Persia, including its culture, language, and people.
Persian
No, old is not a proper adjective. A proper adjective is an adjective derived from a proper noun, such as Swiss cheese, Bolivian pottery, Chinese silk, etc.
Athenian is a proper adjective for Athens.
Egyptian is a proper adjective.
In the sentence "Egypt was conquered by Persia, which was conquered by Alexander the Great," the adjective clause "which was conquered by Alexander the Great" is non-essential. It provides additional information about Persia but is not crucial to understanding the main point of the sentence, which is that Egypt was conquered by Persia. Removing the clause would still leave a complete and coherent sentence.
Persian
The correct spelling of the proper adjective is Scandinavian.
Persia
The likely term is the proper noun, an historical region, Persia (now Iran).
Those letters will spell the proper noun or proper adjective African.
The correct spelling of the proper noun or adjective is Portuguese.
That is the correct spelling of the proper adjective Virginian (from Virginia).
The proper adjective or term for people from China is Chinese.
The correct spelling of the proper noun or adjective is Jamaican.
An adjective describes a noun. You could potentially describe a person or thing as "Vietnamese".
The proper adjective for a person, thing, or characteristic is European (capitalized).
The correct spelling of the proper adjective and demonym is Haitian (of or from Haiti).