In which situation is the object experiencing unbalanced forces?

a box resting on a horizontal floor

a car slowing as it reaches a stop light

a car with its cruise control set to 50 mph

a rocket sitting on the launch pad

The moving car experiences unbalanced forces when applying brakes; when a car is slowing as it reaches a stop light.

When the car driver applies brakes to a car in order to stop, an unbalanced force is applied to the car. The speed of car gradually reduces and there’s a decrease in acceleration; a net force acts on it.

Options A and D has a box and a rocket always in a rest position. A car with cruise control is an adaptable speed setting for a vehicle which helps it to maintain a fairly constant speed. Constant velocity gives zero acceleration and hence no considerable unbalanced forces appear.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."