Impetigo.
Explanation....
It cannot be acne since this occurs when you are more in the teens and is not yellow, eliminate the last one.
It cannot be ringworm because they are worms and not apperanced by yellow crust, eliminate the second one.
It cannot be eczema since this is red not yellow, eliminate the first one.
Impetigo appears as yellow crust. Therefore, your answer is the third one, Impetigo.