Hold a pocket mirror about half an arm’s length from your face and see how much of your face you see in the mirror. To be able to see more of your face, should you hold the mirror closer or farther, or would you have to have a larger mirror?

The size of the mirror must be half of the size of your face.

Explanation:

As we know that pocket mirror is a plane mirror, for the plane mirror, distance of a person from the mirror does not affect the image formed by mirror. But the height of the mirror must be half of the height of the person to see the whole face. It is because pocket mirror is between your head and the virtual image formed, to see the virtual image, your face rays must strike the reflecting surface, for that purpose the size of the mirror must be large enough so that your face rays can strike the reflecting surface easily.