Which type of force can act through empty space?

spring

tension

normal

magnetism

Answer

Magnetism

By empty space we mean in vacuum. A force in a spring means gravity must play part. Force on a spring gravitational force must apply. For this reason it can not act through empty space.

Tension is the force experienced due to compression or extension. In this case gravity is involved and so it can't act through empty space.

Normal force is given by the product of mass and gravity.

Magnetism is the force of attraction or repulsion in magnetism. This is the only force that can act through empty space.  

continuous conducting path for current, power supply