This question tests the Principle of Transmissibility of Forces, one of the foundational assumptions of rigid-body statics. It states that the external effect of a force acting on a rigid body is unchanged if the force is shifted to any other point along its own line of action, provided the magnitude and direction are kept the same.

The external effect of a force on a body is captured entirely by three things: its magnitude, its direction, and its line of action. The overall force and the moment it produces about any chosen point depend only on these, not on the specific point of application along that line. Since the resultant force and resultant moment stay identical, the support reactions and the overall translational/rotational equilibrium of the body do not change.

For the 100 N force, sliding it to another point on the same line of action leaves the equilibrium equations (ΣF = 0 and ΣM = 0) exactly the same, so the external equilibrium remains unchanged.

• The external equilibrium changes is wrong because nothing that governs equilibrium (magnitude, direction, line of action) has been altered.
• The effect depends on the material is wrong for external equilibrium: transmissibility is a rigid-body result independent of material. Material only affects the internal stress distribution, which can indeed change when the point of application moves — but that is a separate, internal issue, not external balance.
• The force magnitude becomes zero is meaningless — relocating a force along its line does not annihilate it.

Therefore the correct answer is that the external equilibrium remains unchanged.