Unfortunately you have not given sufficient detail for a reasonable answer.
Please review your question and re-ask with some details about your problem.
Memory key for what?
What is the make and model of your phone?
Why do you think your memory key is missing?
When did you last see it?
Details about why you are asking would also help.
It is up to you. Keep quiet about the details and get no mend, or help others to help you. The choice is yours.