The reaction force is the force exerted on the ice skater by the railing.
When the ice skater pushes off a railing, the reaction force is the force exerted by the railing back onto the skater. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. So, in this case, the action force is the force exerted by the skater onto the railing, and the reaction force is the force exerted by the railing back onto the skater.
The reaction force to an ice skater pushing off a railing would be the force exerted by the railing on the ice skater. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. So, in this case, as the ice skater pushes off the railing with a force, the railing exerts an equal and opposite force back on the skater, providing the necessary impulse for the skater to move away from the railing. Therefore, the reaction force is the force exerted by the railing on the ice skater.
