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Question
Which of the followings are polyhedron?
Which of the followings are polyhedron?
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Solution
The correct option is C Pyramid
Non-polyhedron: A 3-dimensional solid with at least one curved face.
Polyhedron: A 3-dimensional solid with flat polygonal faces, straight edges and sharp corners or vertices.
Option(a) Like a circle in 2-dimensional space, sphere is an object in 3-dimensional space whose set of points are at equal distance from a fixed point(centre). 
As this 3-dimensional object has curved surface, it can not be a polyhedron.
Option(b): Square is a two-dimensional object, 
hence it can not be a polyhedron.
Option(c): Pyramid is a 3-dimensional object formed by connecting a polygon base with a point.
It is a 3-dimensional solid with flat polygonal faces, straight edges and sharp corners or vertices. Hence, it is a polyhedron.
Option(d): Cone is formed by rotating a triangle taking one of its short sides as axis of rotation.
Cone is 3-dimension object that narrows smoothly from a flat circular base to an apex point. 
It has curved surface hence, it can not be a polyhedron.
Non-polyhedron: A 3-dimensional solid with at least one curved face.
Polyhedron: A 3-dimensional solid with flat polygonal faces, straight edges and sharp corners or vertices.
Option(a) Like a circle in 2-dimensional space, sphere is an object in 3-dimensional space whose set of points are at equal distance from a fixed point(centre).
As this 3-dimensional object has curved surface, it can not be a polyhedron.Option(b): Square is a two-dimensional object,
hence it can not be a polyhedron.Option(c): Pyramid is a 3-dimensional object formed by connecting a polygon base with a point.
It is a 3-dimensional solid with flat polygonal faces, straight edges and sharp corners or vertices. Hence, it is a polyhedron.Option(d): Cone is formed by rotating a triangle taking one of its short sides as axis of rotation.
Cone is 3-dimension object that narrows smoothly from a flat circular base to an apex point.
It has curved surface hence, it can not be a polyhedron.Suggest Corrections
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