Which process is responsible for the greatest loss
of energy from earth’s surface into space on a
clear night?
(1) condensation (3) radiation
(2) conduction (4) convection

I think the correct answer from the choices listed above is option 4. I think it is the process of convection that is responsible for the greatest loss of energy  from Earth’s surface into space on a clear night. Convection happens when a mass which contains heat energy is in motion. This happens in wind blowing, oceanic currents and other naturally occurring fluid flows.