The correct answer is: 1.75
The shape factor is a dimensionless parameter that is used in plastic analysis to determine the load-carrying capacity of a structural member. It is defined as the ratio of the plastic moment of inertia of the cross-section to the elastic moment of inertia of the cross-section.
The plastic moment of inertia is the moment of inertia of the cross-section when it is subjected to a pure bending moment. The elastic moment of inertia is the moment of inertia of the cross-section when it is subjected to a small bending moment.
The shape factor is important because it determines the load-carrying capacity of a structural member. A higher shape factor means that the member can carry a higher load.
The shape factor for a circular section is 1.75. This means that a circular section can carry a load that is 1.75 times the load that a rectangular section of the same area can carry.
The other options are incorrect because they are not the shape factor for a circular section.