The prefix for proper is pro
Use the prefix of Mrs. if it is a fomal letter. If not, and you are familiar with them, use their first name.
It is improper.
what is the proper way to address the mayor
The proper prefix for a female if you don't know if she is married is "Ms." This term can be used for all women, regardless of their marital status.
impure
A hyphen is used to separate a prefix from a proper noun or adjective, especially when the combination could be confusing or misleading without it.
The word "improper" contains the prefix "im-" and the root word "proper." The prefix "im-" typically means "not," so "improper" literally means "not proper." The suffix is not present in this word.
Proper
The prefix "im" is a variant of the prefix "in". It creates the opposite of the original word. Examples are: moveable / immovable; possible / impossible.
Ms.
The proper prefix would be "Ms." "Miss" is for unmarried women. "Mrs." is used for married women. "Ms." is used when marital status is unknown or when the woman does not disclose it intentionally.