Question

Which of the following is responsible for the flow of electrons in a circuit?

electrostatic force

electromotive force

any force exerted by electromagnetic radiation

the force of a magnetic field on a static charge

Answer 1

Think of a circuit. The battery (or power source) creates a potential difference, which is a type of electromotive force (commonly called emf).

Electrostatic force is between single charges, which isn't usually the cause of a circuit.
I'm not sure if EM radiation is, but I think it might work because of the photoelectric effect.
A magnetic field only exerts a force on moving charges.

Therefore, the EMF option seems the best.