Select the properly punctuated sentence.

a.
Please let me know; when I may contact you.
b.
Please let me know, when I may contact you.
c.
Please let me know when I may contact you.

C works for me.

The properly punctuated sentence is option c: "Please let me know when I may contact you."

To determine the correct punctuation, we need to understand the rules for punctuating a sentence. In this case, we are using a declarative sentence structure (making a statement or asking a question).

The first option (a) includes a semicolon (;) which is not appropriate for this sentence structure. Semicolons are typically used to join two closely related independent clauses.

The second option (b) includes a comma (,) before the word "when." While commas are used in various situations, in this case, it is not necessary or appropriate.

The third option (c) does not have any unnecessary punctuation. It simply has a space between the words "know" and "when," which is correct for this sentence structure.

Therefore, option c is the correctly punctuated sentence.