Question

which part of a formal e - mail is optional?
○ the closing
○ the contact information
○ the persons last name
○ the salutation

Explanation:

In a formal email, the salutation (e.g., "Dear [Name],") can sometimes be optional in very informal or quick formal communications, while the closing (e.g., "Sincerely"), contact information, and the person’s last name (in addressing) are more standard or necessary. The contact information is important for the recipient to reply, the closing is a standard part, and the last name in salutation is common for formality. The salutation can be skipped in some brief formal emails.

Answer:

the salutation