Answer: A point or a circle with radius less than or equal to the radius of the base of the cone.
Step-by-step explanation: As shown in the attached figure, a horizontal plane is passing through a cone with horizontal base, so, the base of the cone and the plane are parallel to each other.
(i) If the horizontal plane is at the tip of the cone, the it will produce just a point.
(ii) If the plane passes through the cone , then the intersection will be a circle, where the radius can be less than or equal to the radius of the base of the cone.
(iii) If the plane coincides with the base of the cone, then the intersection will be a circle with radius equal to the radius of the base of the cone.
Thus, the intersection will produce either a point or a circle.
