The correct answer is (a) convex.
A convex mirror is a curved mirror that bulges outward at the center. It forms a virtual image that is upright and smaller than the object. This type of mirror is often used in dentists’ offices to allow dentists to see the back of patients’ teeth.
A concave mirror is a curved mirror that bulges inward at the center. It forms a real image that is upright and larger than the object. This type of mirror is often used in telescopes and microscopes to magnify objects.
A plane mirror is a flat mirror. It forms a virtual image that is upright and the same size as the object. This type of mirror is often used in bathrooms and bedrooms to allow people to see themselves.
I hope this helps!