A car of mass 900 kg pulls a caravan of mass 400 kg along a straight, horizontal road with an acceleration of 2.0 ms⁻². Assuming that the frictional forces on the caravan are negligible, the tension in the coupling between the car and the caravan is

The mass of the caravan is $m = 400 \text{ kg}$.
The acceleration of the system (car and caravan) is $a = 2.0 \text{ m/s}^2$.
Frictional forces on the caravan are negligible.

The tension in the coupling ($T$) is the net force acting on the caravan in the direction of motion, as frictional forces are negligible. According to Newton's Second Law, $F = ma$.

The tension in the coupling is $800 \text{ N}$. This corresponds to option C.

The final answer is $\text{C}$.