Question

multiple choice question
an isolated system is a closed system on which the net

gravitational force is zero
unbalanced force is zero,
internal force is zero
external force is zero

Explanation:

To determine the correct option, we analyze the definition of an isolated system in physics (a subfield of Natural Science). An isolated system is one where no external forces act on it, meaning the net external force is zero. Gravitational force being zero is too specific (isolated systems can still have gravity, but no net external forces). Unbalanced force relates to motion but isn't the definition of an isolated system. Internal forces don't define an isolated system as internal forces act within the system. So the correct option is about net external force being zero.

Answer:

D. external force is zero